feat(workspace): one global switcher anchor in the shell sidebar

The switcher used to be embedded per page (Flows/Runs/Audit/
Approvals) — invisible on the other five pages and sitting in a
different corner depending on the page (persona review 2026-08-27,
consensus finding). It now lives ONCE in the sidebar, above the
destinations: active project/area always visible, opens the same
menu everywhere, Cmd+P from anywhere. The shell listens to the
workspace, so the sidebar endpoint label can no longer lag a
sealed switch until the next health tick.

Also in this rebuild:

* Stopped sealed areas ask before starting ("Start area X?") —
  a context switch must never boot a hub daemon as a click
  side-effect; running areas keep switching with one click.
* The switcher tooltip told a wrong scope ("filters this view") —
  it now says the choice applies everywhere and stamps new runs.
* The aggregated sealed row explains itself in place (names can
  reveal client identities) and links to the Settings toggle
  (Settings dialog gained an initialCategory jump).
* The active entry carries a checkmark in the menu.
* The Cmd+K palette knows projects and areas, ranked by recent
  use; sealed names honour the privacy setting — while hidden,
  the palette offers the guarded picker instead of the names.
* The runs empty state names the active project filter as the
  cause ("No runs in project X" + show-all action) instead of
  claiming the feature is off.

Tests updated to the anchor and made hermetic (scriptable
projects on the fake hub, sealed-area fake); new coverage for the
checkmark, the why-line, and the start confirmation.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/pages/approvals.dart

@@ -376,8 +376,6 @@ class _ApprovalsPageState extends State<ApprovalsPage> {
           ),
         ),
         actions: [
-          const ChainWorkspaceSwitcher(),
-          const SizedBox(width: ChainSpace.md),
           IconButton(
             icon: const Icon(Icons.help_outline, size: 18),
             tooltip: AppLocalizations.of(context)!.helpTooltip,