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/settings-jump-contract

@@ -63,8 +63,8 @@ done
 # contextual affordances must retain the original interaction and route to the
 # setting page that owns the controls.
 [[ -r "$dock_menu" ]] || fail 'dock has no contextual menu, so application actions cannot keep a final Dock settings action'
-grep -qF 'ShellState.openSettings("desktop")' "$dock_menu" \
-    || fail 'dock context menu does not open Desktop settings'
+grep -qF 'ShellState.openSettings("dock")' "$dock_menu" \
+    || fail 'dock context menu does not open Dock settings'
 grep -qF 'entry.actions' "$dock_menu" \
     || fail 'dock context menu dropped application actions'
 actions_line="$(grep -nF 'entry.actions' "$dock_menu" | head -1 | cut -d: -f1)"