feat: workspace switcher, per-project filters and run stamping (stage 1)

Multi-project stage 1 against the shared hub (platform design
docs/architecture/projects.md, § Studio):

- ChainWorkspaceSwitcher in the Audit + Approvals AppBars: lists the
  registry (colour dot per project, shield for protected, honesty
  tooltip), 'All projects' stays reachable — a filter, not a jail.
  Selection is persisted and shared via the Workspace notifier.
- Audit page: list query AND live stream re-scoped hub-side on switch.
- Approvals page: pending + history scoped; the sidebar badge counts
  the active workspace's pending approvals.
- Flow runs are stamped with the active workspace; a flow file
  carrying its own project: keeps it (file wins, CLI semantics).
- Data layer: listProjects/ProjectRef; project fields on AuditEvent,
  PendingApproval(+Record), SavedFlow; project params through
  HubService. l10n DE+EN. Widget tests for the switcher contract.

Visual verification (light+dark screenshots) still pending — the
shared desktop was in active use; code paths are covered by
flutter test (26 green).

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

lib/l10n/app_localizations.dart

@@ -4890,6 +4890,24 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Hand the token to the satellite operator over a secure channel. The bundled CA authenticates the satellite\'s first connect.'**
   String get federationEnrollmentHint;
+
+  /// No description provided for @workspaceAll.
+  ///
+  /// In en, this message translates to:
+  /// **'All projects'**
+  String get workspaceAll;
+
+  /// No description provided for @workspaceSwitcherTooltip.
+  ///
+  /// In en, this message translates to:
+  /// **'Workspace — filters this view and stamps new runs with the selected project'**
+  String get workspaceSwitcherTooltip;
+
+  /// No description provided for @workspaceProtectedHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Protected: logically separated in the shared hub — no hard process barrier. Critical engagements use a sealed area.'**
+  String get workspaceProtectedHint;
 }
 
 class _AppLocalizationsDelegate