feat(audio-player): gear-menu default speed + split shortcuts into Mouse/Touch (plan §12)

The Player settings popover gains a 'Default playback speed' row
beside autoplay — a compact rate select, always visible (the Speed ▾
footer hides when current == default, which made the setting
undiscoverable at 1x/1×); same setDefaultSpeed PUT. The shortcuts
dialog splits its pointer section into MOUSE (click/drag/shift/wheel)
and TOUCH (drag/pull-away) — the bar has two scrub systems and the
sections now say so.

web/src/audio.ts

@@ -15,7 +15,13 @@
 import { Alpine } from "./alpine";
 import { renderNoteHtml } from "./markdown";
 import { showToast } from "./toast";
-import { POINTER_GUIDE, resolveShortcut, visibleKeymap, type KeyAction } from "./audio-keys";
+import {
+  MOUSE_GUIDE,
+  resolveShortcut,
+  TOUCH_GUIDE,
+  visibleKeymap,
+  type KeyAction,
+} from "./audio-keys";
 import {
   SLEEP_CHOICES,
   SLEEP_OFF,
@@ -202,8 +208,9 @@ Alpine.data("audioReader", () => ({
   // Exposed for the templ dropdown's x-for — templ cannot import the
   // const directly; this property is the binding.
   speeds: SPEEDS,
-  // Same binding pattern, for the dialog's Mouse & touch section.
-  pointerGuide: POINTER_GUIDE,
+  // Same binding pattern, for the dialog's two scrub-system sections.
+  mouseGuide: MOUSE_GUIDE,
+  touchGuide: TOUCH_GUIDE,
   skipSeconds: Number(localStorage.getItem("audio_skip") || 10),
   // End-label display mode (§10): total → book remaining → chapter
   // remaining, persisted per device.