feat(stats): Library tab — per-library inventory stats + audio-aware Reading tab

The /stats page gains a second tab (Reading | Library) implementing the
Audiobookshelf-style library dashboard (HANDOFF item 9): media_items
INVENTORY aggregates — items, hours/pages, distinct authors, size,
distinct narrators, Top Genres / Top Authors bars, Longest / Largest
items — for one library or the All-libraries aggregate.

- GET /api/stats/library-usage?library_id=<uuid|omit>; family lens
  enforced: a library_id outside the requester's visible set is a 403,
  never a silent pass (AGENTS.md standing rule; 431fec0 history)
- six sqlc queries with the visibility pattern + healthy-item filter
  (archived_at IS NULL AND missing_scan_count = 0); hours_mode lets the
  client swap the Hours/Pages card and the Longest ranking per scope
- Reading tab unit audit (HANDOFF item 3, settled 2026-10-16): minutes
  are the merged currency everywhere honest; only the PAGES unit splits
  — Pages card goes mode-aware (Pages · text / Listening Time in an
  audio-only pool) and the charts row gains Listening per Day (hrs)
  when audio minutes exist in the range; summary daily buckets gain
  audio_minutes split by the item's library type
- tab state in the URL (?tab=library&library_id=…); selector fed by the
  existing /api/libraries/visibility endpoint; main.js?v=4
- integration tests: family-lens 403 pin, hidden-library exclusion
  (differential), seeded text+audio aggregate correctness, auth gate
- docs/developer/api/stats/get_library_usage.md

Known-remaining suite failures are environmental: TestConflictList_Empty
+ TestWebSocketPingPong collide with the concurrently-running app session
(live emulator pushes + scans on the shared dev DB), and
TestAdminCreateUser's timezone expectation drifted from live system
settings — all three fail on the clean tree too.

templates/stats_templ.go

@@ -58,7 +58,7 @@ func Stats(user User) templ.Component {
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}
-		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 4, ") · totals derive from your devices' sync pushes, not a stopwatch.</p></div><div class=\"card p-4 mb-6 flex flex-wrap items-center justify-between gap-3\"><div class=\"flex gap-2\" id=\"stats-range-selector\"><button data-range=\"7\" @click=\"selectRange('7')\" class=\"stats-range-btn btn btn-secondary text-sm\">Last 7 days</button> <button data-range=\"30\" @click=\"selectRange('30')\" class=\"stats-range-btn btn btn-secondary text-sm\">30 days</button> <button data-range=\"90\" @click=\"selectRange('90')\" class=\"stats-range-btn btn btn-secondary text-sm\">90 days</button> <button data-range=\"year\" @click=\"selectRange('year')\" class=\"stats-range-btn btn btn-secondary text-sm\">This year</button></div><p class=\"text-xs\" style=\"color: var(--text-secondary)\" id=\"stats-window-label\"></p></div><div class=\"grid grid-cols-2 lg:grid-cols-5 gap-4 mb-8\"><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Reading Time</h3><p id=\"stats-total-minutes\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Pages</h3><p id=\"stats-total-pages\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Streaks</h3><p id=\"stats-streaks\" class=\"text-lg font-bold leading-tight mt-1\" style=\"color: var(--text-primary)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Books Finished</h3><p id=\"stats-books-finished\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Most Active</h3><p id=\"stats-most-active\" class=\"text-sm font-bold leading-snug mt-2\" style=\"color: var(--text-primary)\">–</p></div></div><div class=\"grid grid-cols-1 lg:grid-cols-2 gap-6 mb-8\"><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Daily Reading Minutes</h3><div class=\"h-64\"><canvas id=\"stats-daily-minutes-chart\"></canvas></div></div><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Pages per Day</h3><div class=\"h-64\"><canvas id=\"stats-daily-pages-chart\"></canvas></div></div></div><div class=\"grid grid-cols-1 lg:grid-cols-3 gap-6 mb-8\"><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">By Library</h3><div id=\"stats-library-breakdown\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">By Device</h3><p class=\"text-xs mb-3\" style=\"color: var(--text-secondary)\">Where the sync pushes came from — registered device names, plus a Web bucket for pushes that carry no device credential (the web reader).</p><div id=\"stats-device-breakdown\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Most Read</h3><div id=\"stats-top-books\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div></div><div id=\"stats-empty\" class=\"card p-8 text-center hidden\"><p class=\"text-sm mb-2\" style=\"color: var(--text-primary)\">No reading sessions recorded in this range yet.</p><p class=\"text-xs\" style=\"color: var(--text-secondary)\">Sessions are captured every time a device syncs reading progress (KOReader, the app, the web reader).</p></div></div>")
+		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 4, ") · totals derive from your devices' sync pushes, not a stopwatch.</p><div class=\"flex gap-2 mt-4\" id=\"stats-tab-row\"><button data-tab=\"reading\" @click=\"selectTab('reading')\" class=\"stats-tab-btn btn btn-secondary text-sm\">Reading</button> <button data-tab=\"library\" @click=\"selectTab('library')\" class=\"stats-tab-btn btn btn-secondary text-sm\">Library</button></div></div><!-- READING tab — behavior stats from sync pushes (all libraries) --><div id=\"stats-reading-section\"><div class=\"card p-4 mb-6 flex flex-wrap items-center justify-between gap-3\"><div class=\"flex gap-2\" id=\"stats-range-selector\"><button data-range=\"7\" @click=\"selectRange('7')\" class=\"stats-range-btn btn btn-secondary text-sm\">Last 7 days</button> <button data-range=\"30\" @click=\"selectRange('30')\" class=\"stats-range-btn btn btn-secondary text-sm\">30 days</button> <button data-range=\"90\" @click=\"selectRange('90')\" class=\"stats-range-btn btn btn-secondary text-sm\">90 days</button> <button data-range=\"year\" @click=\"selectRange('year')\" class=\"stats-range-btn btn btn-secondary text-sm\">This year</button></div><p class=\"text-xs\" style=\"color: var(--text-secondary)\" id=\"stats-window-label\"></p></div><div class=\"grid grid-cols-2 lg:grid-cols-5 gap-4 mb-8\"><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Reading Time</h3><p id=\"stats-total-minutes\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\" id=\"stats-pages-card-label\">Pages</h3><p id=\"stats-total-pages\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Streaks</h3><p id=\"stats-streaks\" class=\"text-lg font-bold leading-tight mt-1\" style=\"color: var(--text-primary)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Books Finished</h3><p id=\"stats-books-finished\" class=\"text-3xl font-bold\" style=\"color: var(--accent)\">–</p></div><div class=\"stat-card\"><h3 class=\"text-xs font-semibold uppercase tracking-wide mb-2\" style=\"color: var(--text-secondary)\">Most Active</h3><p id=\"stats-most-active\" class=\"text-sm font-bold leading-snug mt-2\" style=\"color: var(--text-primary)\">–</p></div></div><div class=\"grid grid-cols-1 lg:grid-cols-3 gap-6 mb-8\"><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Daily Reading Minutes</h3><div class=\"h-64\"><canvas id=\"stats-daily-minutes-chart\"></canvas></div></div><div class=\"card p-6\" id=\"stats-pages-chart-panel\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\" id=\"stats-pages-chart-label\">Pages per Day</h3><div class=\"h-64\"><canvas id=\"stats-daily-pages-chart\"></canvas></div></div><div class=\"card p-6 hidden\" id=\"stats-listening-chart-panel\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Listening per Day (hrs)</h3><div class=\"h-64\"><canvas id=\"stats-daily-listening-chart\"></canvas></div></div></div><div class=\"grid grid-cols-1 lg:grid-cols-3 gap-6 mb-8\"><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">By Library</h3><div id=\"stats-library-breakdown\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">By Device</h3><p class=\"text-xs mb-3\" style=\"color: var(--text-secondary)\">Where the sync pushes came from — registered device names, plus a Web bucket for pushes that carry no device credential (the web reader).</p><div id=\"stats-device-breakdown\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div><div class=\"card p-6\"><h3 class=\"text-sm font-semibold uppercase tracking-wide mb-4\" style=\"color: var(--text-secondary)\">Most Read</h3><div id=\"stats-top-books\" class=\"space-y-3\"><div class=\"text-center py-6 text-sm\" style=\"color: var(--text-secondary)\">Loading…</div></div></div></div><div id=\"stats-empty\" class=\"card p-8 text-center hidden\"><p class=\"text-sm mb-2\" style=\"color: var(--text-primary)\">No reading sessions recorded in this range yet.</p><p class=\"text-xs\" style=\"color: var(--text-secondary)\">Sessions are captured every time a deviLine truncated
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}