feat: detached-runs monitor page (T3 parity)

New Runs sidebar destination listing detached invocations (detach:true)
with phase, current step, project and a Cancel button while
pending/running. Workspace-scoped like Audit/Approvals, polls every 2s.
Detached runs are opt-in (detached.enabled) — the empty state explains
how to enable them. Inline help doc DE+EN. DetachedRun model +
listDetachedRuns/cancelDetachedRun in HubService, backed by the SDK's
listInvocations()/cancelInvocation(). flutter analyze clean; 29 tests
green (sidebar Y-stability updated for the new destination, model
mapping unit-tested).

Screenshot verification (light+dark) deferred — shared desktop in use.

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

lib/main.dart

@@ -21,6 +21,7 @@ import 'pages/audit.dart';
 import 'pages/doctor.dart';
 import 'pages/federation.dart';
 import 'pages/flows.dart';
+import 'pages/runs.dart';
 import 'pages/store.dart';
 import 'pages/welcome.dart';
 import 'theme/theme.dart';
@@ -380,6 +381,12 @@ class StudioShellState extends State<StudioShell> {
       selectedIcon: Icons.inbox,
       page: ApprovalsPage(),
     ),
+    _NavPage(
+      id: 'runs',
+      icon: Icons.rocket_launch_outlined,
+      selectedIcon: Icons.rocket_launch,
+      page: RunsPage(),
+    ),
     _NavPage(
       id: 'federation',
       icon: Icons.hub_outlined,
@@ -1641,6 +1648,8 @@ class _NavPage {
         return l.navAudit;
       case 'approvals':
         return l.navApprovals;
+      case 'runs':
+        return l.navRuns;
       case 'federation':
         return l.navFederation;
       default: