Make Shell a category, the bar legible, and the dock a real dock

Desktop & Dock becomes Shell — Bar, Dock, Control Center, Tiling,
Workspaces — the home for everything Quickshell draws. The settings-
management cluster moves to System as Sync & Backup, Appearance's
Shell tab dissolves, and 24-hour time finally lives on Date & Time,
which always owned it.

The bar gets what it never had: a way to survive the wallpaper. A
second neutral text family (follow theme, or forced light or dark),
a one-layer shadow under every glyph, and a gradient scrim for
wallpapers nothing else survives — all off by default, pixel-identical
until asked. Widgets earn toggles (weather, media, clipboard, calendar
countdown), the vitals cluster stops leaving a dead pill behind, and
Control Center's sections learn to step aside.

The dock graduates from MVP: a context menu with window rows, pin,
unpin, quit and new-window; scroll an icon to cycle its windows; drag
to reorder on the dock itself; hover previews with one-shot captures;
and "Add App to Dock" in the launcher. Three real bugs died en route —
menus that slid away with the autohide, a readonly-property crash on
every menu open, and a drag that drifted half a slot per icon on side
docks. The pinned-apps editor in Settings becomes a drag strip.

166 contracts; the full suite is green except two live display and
switcher tests that cannot run behind a locked session — re-verified
on unlock.

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

tests/quickshell/video-wallpaper-contract

@@ -88,7 +88,7 @@ for reason in ("root.manuallyPaused", "root.gamePaused", "root.batteryPaused"):
 
 # The pause reaches mpv over its JSON IPC socket rather than by killing and
 # respawning the player, which would restart the video from the first frame.
-if 'JSON.stringify({ command: ["set_property", "pause", root.paused] })' not in stripped:
+if 'JSON.stringify({ "command": ["set_property", "pause", root.paused] })' not in stripped:
     raise SystemExit("pausing no longer goes over mpv's JSON IPC")
 if 'onPausedChanged: pauseSync.restart()' not in stripped:
     raise SystemExit("a change of pause state does not push to the player")
@@ -122,7 +122,7 @@ rg -Fq 'mpvpaper' "$packages" \
 # reasoned about per output.
 rg -Fq 'playerRespawn.restart();' "$service" \
     || fail 'a crashed player is not respawned'
-rg -Fq 'onOutputsChanged: if (root.active) playerRespawn.restart()' "$service" \
+rg -Fq 'onOutputSignatureChanged: if (root.active) playerRespawn.restart()' "$service" \
     || fail 'a display hotplug does not respawn the players'
 
 # ── 3. The hyprpaper handover ───────────────────────────────────────────────