web: music dock joins the layout flow — removes the nav-dock overlap hacks

The music dock was position:fixed, overlaying the bottom of the content, so the
nav dock needed a pile of hacks to dodge it: a hand-measured MUSIC_DOCK_HEIGHT
(72) constant, a presence flag, a translateY lift, and a matching hover-threshold
lift (via a ref) so it wouldn't slide away under the cursor. Fragile the moment
the music dock's height changed.

Now the dock is an in-flow bottom bar that reserves its own height:
- DashboardLayout is a flex column: the content region (flex-1, min-h-0) shrinks
  when the music dock takes its space; MusicPlayerHost renders an in-flow bar
  (shrink-0) instead of a fixed overlay.
- The nav Dock is absolute within the content region and measures its reveal/hide
  boundary from that region's bottom edge (a boundaryRef) — so it always sits just
  above whatever's at the bottom, music dock or not, with zero knowledge of it.
- Deleted MUSIC_DOCK_HEIGHT, musicDockPresent, the lift, and the transform hack.

Bonus: content at the very bottom is no longer hidden under the fixed dock.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/workspaces/officerdev/src/MusicPlayer/MusicPlayerHost.tsx

@@ -249,8 +249,10 @@ export const MusicPlayerHost = () => {
 
   if (!current) return null;
 
+  // In-flow bottom bar (NOT position:fixed) — it reserves its own height so the content above shrinks to
+  // fit and the nav dock naturally sits above it, no overlap hacks needed.
   return (
-    <div className="fixed inset-x-0 bottom-0 z-50 flex items-center gap-3 border-t border-border bg-card/95 px-4 py-2 backdrop-blur">
+    <div className="flex shrink-0 items-center gap-3 border-t border-border bg-card/95 px-4 py-2 backdrop-blur">
       {/* cover + info — click to open this album in /music */}
       <button
         type="button"

src/workspaces/officerdev/src/MusicPlayer/useMusicPlayer.ts

@@ -19,9 +19,6 @@ export type MusicPlayerState = {
 
 const INITIAL: MusicPlayerState = { queue: [], index: 0, playing: false };
 
-// Amount (px) the nav Dock shifts up while the music dock is present, so it clears it.
-export const MUSIC_DOCK_HEIGHT = 72;
-
 export function useMusicPlayer() {
   const [state, setState] = useGlobal<MusicPlayerState>('MUSIC_PLAYER', INITIAL);