feat(audio-player): per-book playback speed + user default (plan §8)

Speed becomes a per-USER-per-BOOK preference that syncs across
devices, with a user-level default for books not yet played:
- new audio_playback_speed table (mirrors reading_speed's shape; a
  preference, NOT a measurement and NOT a reading_progress column) +
  users.default_audio_speed, schema in place
- chapters endpoint resolves per-book row → user default → 1.0 and
  ships playback_speed + default_playback_speed (zero extra round
  trips; default powers the dropdown marker)
- PUT /api/media-items/:id/audio-speed upserts (range-checked; the
  client SPEEDS list stays the real gate; library visibility gates
  writes)
- the user default rides the profile path like theme/timezone:
  profile form gains a 'Default Playback Speed' select (server-side
  SpeedOptions mirrors the web SPEEDS list), GET /profile carries it
- web: restorePosition applies the resolved server speed (localStorage
  audio_speed demotes to a first-paint cache); setSpeed PUTs
  fire-and-forget with a failure toast; the Speed dropdown gains a
  '(default)' row marker and a 'Make N× my default' action with a
  success toast

ALSO fixes a pre-existing profile-page bug surfaced by the §8 form
verification: the password section's current_password input was
required INSIDE the shared form, so HTML5 validation blocked every
Save Changes submission (dead since the shell migration). The
password flow keeps its own gates (disabled-button checkers + server
400).

Integration test TestAudioPlaybackSpeed pins the full contract (unset
→ 1x, upsert resolution, range rejection, default fallback for
row-less books, default updates re-satisfying unset books). Verified
live: 9 Playwright checks.

templates/audio_reader_templ.go

@@ -194,7 +194,7 @@ func AudioReader(user User, metadata ReaderMetadata) templ.Component {
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}
-		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 15, "</h1><p class=\"text-sm mt-0.5 truncate\" style=\"color: var(--text-secondary);\" x-text=\"chapterTitle()\">—</p></div></div><!-- Scrubber + transports --><div class=\"w-full max-w-xl flex flex-col gap-2\"><div class=\"flex items-center gap-2 text-xs tabular-nums\" style=\"color: var(--text-secondary);\"><span class=\"inline-block min-w-[4.75rem]\" x-text=\"fmtTime(scrubbing ? scrubValue : currentTime)\">0:00</span><div id=\"scrub-area\" class=\"relative flex-1 h-6 flex items-center cursor-pointer\" style=\"touch-action: none;\" @pointerdown=\"scrubPointerDown($event)\" @pointermove=\"scrubPointerMove($event)\" @pointerup=\"scrubPointerUp($event)\" @pointercancel=\"scrubPointerUp($event)\" @pointerleave=\"scrubPointerLeave()\" @wheel.prevent=\"onScrubWheel($event)\"><!-- Base track --><div class=\"absolute inset-x-0 top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" style=\"background-color: var(--surface-hover);\"></div><!-- Elapsed fill --><div class=\"absolute top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" :style=\"'left:0;width:' + scrubFillPct() + '%;background-color:var(--accent);'\"></div><!-- Buffered span: the ACTIVE track's element buffer only --><template x-if=\"bufferSpan()\"><div class=\"absolute top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" :style=\"'left:' + bufferSpan().left + '%;width:' + bufferSpan().width + '%;background-color:var(--accent-muted);'\"></div></template><!-- Chapter ticks: density-decimated, current chapter tinted --><div id=\"scrub-ticks\" class=\"absolute inset-0 pointer-events-none\"><template x-for=\"idx in tickIndices\" :key=\"'tick' + idx\"><div class=\"absolute top-1/2 -translate-x-1/2 -translate-y-1/2 h-2 w-0.5 rounded-full\" :class=\"currentChapterIdx === idx ? 'opacity-100' : 'opacity-40'\" :style=\"'left:' + (chapters[idx].start / (chaptersDuration() || 1) * 100) + '%;background-color:' + (currentChapterIdx === idx ? 'var(--accent)' : 'var(--text-secondary)') + ';'\"></div></template></div><!-- §9 magnet: the line a click would land on (hover\n\t\t\t\t\t\t     inside the pixel radius locks the tooltip here) --><div x-show=\"hoverSnapped && !scrubbing\" x-cloak class=\"absolute top-1/2 -translate-x-1/2 -translate-y-1/2 h-4 w-px rounded-full pointer-events-none\" :style=\"'left:' + hoverPct + '%;background-color:var(--accent);'\"></div><input id=\"audio-scrub\" type=\"range\" min=\"0\" step=\"0.1\" :max=\"chaptersDuration() || 1\" :value=\"scrubbing ? scrubValue : currentTime\" class=\"relative w-full\" @input=\"scrubbing = true; scrubValue = Number($event.target.value)\" @change=\"seekTo(scrubValue); scrubbing = false\" aria-label=\"Seek position\"><!-- Hover tooltip: time + chapter under the pointer --><div x-show=\"hoverSeconds !== null && !scrubbing\" x-cloak class=\"absolute bottom-full mb-1 -translate-x-1/2 whitespace-nowrap rounded-md px-2 py-1 text-[11px] shadow-lg pointer-events-none\" :style=\"'left:' + hoverPct + '%;background-color:var(--bg-secondary);border:1px solid var(--border);color:var(--text-primary);'\"><span x-text=\"hoverSeconds !== null ? fmtTime(hoverSeconds) : ''\"></span> <span style=\"color: var(--text-secondary);\" x-text=\"hoverSeconds !== null ? ' — ' + chapterTitleAt(hoverSeconds) : ''\"></span></div><!-- Precision rail (§9): Shift+drag on mouse, or a touch\n\t\t\t\t\t\t     drag pulled off the bar — ±5 min or tighter, free\n\t\t\t\t\t\t     mapping inside. Edge labels self-document the window\n\t\t\t\t\t\t     (floats over the transports, page never shifts) --><div x-show=\"railVisible\" x-cloak class=\"absolute top-full mt-1 inset-x-0 h-12 rounded-lg shadow-lg p-1.5 pointer-events-none\" :style=\"'background-color: var(--bg-secondary); border: 1px solid var(--border); z-index: 30;' + (railLiftY ? ' transform: translateY(' + railLiftY + 'px);' : '')\"><div class=\"relative h-full\"><div class=\"absolute inset-x-0 top-1/2 h-px\" style=\"background-color: var(--border);\"></div><template x-for=\"tick in railTickList\" :key=\"'rtick' + tick.start\"><div class=\"absolute top-1 bottom-1 w-px\" :style=\"'left:' + ((tick.start - railFrom) / Math.max(1, railTo - railFrom) * 100) + '%;background-color:var(--text-secondary);opacity:0.5;'\"></div></template><div class=\"absolute top-0 bottom-0 w-0.5 -translate-x-1/2 rounded-full\" :style=\"'left:' + railMarkerPct() + '%;background-color:var(--accent);'\"></div><div class=\"absolute left-1 top-0.5 text-[10px] tabular-nums whitespace-nowrap\" style=\"color: var(--text-primary);\" x-text=\"fmtTime(scrubValue) + ' — ' + chapterTitleAt(scrubValue)\"></div><div class=\"absolute left-1 bottom-0.5 text-[9px] tabular-nums\" style=\"color: var(--text-secondary);\" x-text=\"fmtTime(railFrom)\"></div><div class=\"absolute right-1 bottom-0.5 text-[9px] tabular-nums\" style=\"color: var(--text-secondary);\" x-text=\"fmtTime(railTo)\"></div></div></div></div><button typeLine truncated
+		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 15, "</h1><p class=\"text-sm mt-0.5 truncate\" style=\"color: var(--text-secondary);\" x-text=\"chapterTitle()\">—</p></div></div><!-- Scrubber + transports --><div class=\"w-full max-w-xl flex flex-col gap-2\"><div class=\"flex items-center gap-2 text-xs tabular-nums\" style=\"color: var(--text-secondary);\"><span class=\"inline-block min-w-[4.75rem]\" x-text=\"fmtTime(scrubbing ? scrubValue : currentTime)\">0:00</span><div id=\"scrub-area\" class=\"relative flex-1 h-6 flex items-center cursor-pointer\" style=\"touch-action: none;\" @pointerdown=\"scrubPointerDown($event)\" @pointermove=\"scrubPointerMove($event)\" @pointerup=\"scrubPointerUp($event)\" @pointercancel=\"scrubPointerUp($event)\" @pointerleave=\"scrubPointerLeave()\" @wheel.prevent=\"onScrubWheel($event)\"><!-- Base track --><div class=\"absolute inset-x-0 top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" style=\"background-color: var(--surface-hover);\"></div><!-- Elapsed fill --><div class=\"absolute top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" :style=\"'left:0;width:' + scrubFillPct() + '%;background-color:var(--accent);'\"></div><!-- Buffered span: the ACTIVE track's element buffer only --><template x-if=\"bufferSpan()\"><div class=\"absolute top-1/2 -translate-y-1/2 h-1.5 rounded-full pointer-events-none\" :style=\"'left:' + bufferSpan().left + '%;width:' + bufferSpan().width + '%;background-color:var(--accent-muted);'\"></div></template><!-- Chapter ticks: density-decimated, current chapter tinted --><div id=\"scrub-ticks\" class=\"absolute inset-0 pointer-events-none\"><template x-for=\"idx in tickIndices\" :key=\"'tick' + idx\"><div class=\"absolute top-1/2 -translate-x-1/2 -translate-y-1/2 h-2 w-0.5 rounded-full\" :class=\"currentChapterIdx === idx ? 'opacity-100' : 'opacity-40'\" :style=\"'left:' + (chapters[idx].start / (chaptersDuration() || 1) * 100) + '%;background-color:' + (currentChapterIdx === idx ? 'var(--accent)' : 'var(--text-secondary)') + ';'\"></div></template></div><!-- §9 magnet: the line a click would land on (hover\n\t\t\t\t\t\t     inside the pixel radius locks the tooltip here) --><div x-show=\"hoverSnapped && !scrubbing\" x-cloak class=\"absolute top-1/2 -translate-x-1/2 -translate-y-1/2 h-4 w-px rounded-full pointer-events-none\" :style=\"'left:' + hoverPct + '%;background-color:var(--accent);'\"></div><input id=\"audio-scrub\" type=\"range\" min=\"0\" step=\"0.1\" :max=\"chaptersDuration() || 1\" :value=\"scrubbing ? scrubValue : currentTime\" class=\"relative w-full\" @input=\"scrubbing = true; scrubValue = Number($event.target.value)\" @change=\"seekTo(scrubValue); scrubbing = false\" aria-label=\"Seek position\"><!-- Hover tooltip: time + chapter under the pointer --><div x-show=\"hoverSeconds !== null && !scrubbing\" x-cloak class=\"absolute bottom-full mb-1 -translate-x-1/2 whitespace-nowrap rounded-md px-2 py-1 text-[11px] shadow-lg pointer-events-none\" :style=\"'left:' + hoverPct + '%;background-color:var(--bg-secondary);border:1px solid var(--border);color:var(--text-primary);'\"><span x-text=\"hoverSeconds !== null ? fmtTime(hoverSeconds) : ''\"></span> <span style=\"color: var(--text-secondary);\" x-text=\"hoverSeconds !== null ? ' — ' + chapterTitleAt(hoverSeconds) : ''\"></span></div><!-- Precision rail (§9): Shift+drag on mouse, or a touch\n\t\t\t\t\t\t     drag pulled off the bar — ±5 min or tighter, free\n\t\t\t\t\t\t     mapping inside. Edge labels self-document the window\n\t\t\t\t\t\t     (floats over the transports, page never shifts) --><div x-show=\"railVisible\" x-cloak class=\"absolute top-full mt-1 inset-x-0 h-12 rounded-lg shadow-lg p-1.5 pointer-events-none\" :style=\"'background-color: var(--bg-secondary); border: 1px solid var(--border); z-index: 30;' + (railLiftY ? ' transform: translateY(' + railLiftY + 'px);' : '')\"><div class=\"relative h-full\"><div class=\"absolute inset-x-0 top-1/2 h-px\" style=\"background-color: var(--border);\"></div><template x-for=\"tick in railTickList\" :key=\"'rtick' + tick.start\"><div class=\"absolute top-1 bottom-1 w-px\" :style=\"'left:' + ((tick.start - railFrom) / Math.max(1, railTo - railFrom) * 100) + '%;background-color:var(--text-secondary);opacity:0.5;'\"></div></template><div class=\"absolute top-0 bottom-0 w-0.5 -translate-x-1/2 rounded-full\" :style=\"'left:' + railMarkerPct() + '%;background-color:var(--accent);'\"></div><div class=\"absolute left-1 top-0.5 text-[10px] tabular-nums whitespace-nowrap\" style=\"color: var(--text-primary);\" x-text=\"fmtTime(scrubValue) + ' — ' + chapterTitleAt(scrubValue)\"></div><div class=\"absolute left-1 bottom-0.5 text-[9px] tabular-nums\" style=\"color: var(--text-secondary);\" x-text=\"fmtTime(railFrom)\"></div><div class=\"absolute right-1 bottom-0.5 text-[9px] tabular-nums\" style=\"color: var(--text-secondary);\" x-text=\"fmtTime(railTo)\"></div></div></div></div><button typeLine truncated
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}