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

config/dot/quickshell/modules/bar/MediaWidget.qml

@@ -29,7 +29,7 @@ Pill {
         return artist ? artist + " — " + title : title;
     }
 
-    visible: root.player !== null
+    visible: Settings.showMediaWidget && root.player !== null
     horizontalPadding: 8
 
     onActivated: if (root.player?.canTogglePlaying)
@@ -63,7 +63,7 @@ Pill {
         text: root.label
         font.family: Theme.fontFamily
         font.pixelSize: Theme.fontSize
-        color: Theme.fg
+        color: Theme.barFg
 
         // Titles are unbounded; the bar is not. Elide rather than let one
         // podcast episode push the tray off the edge.