feat: maintenance flow UX redesign — batch status hub, context strip, detail page upgrades (#85)

- Add BatchStatusPage (/flows/:id/batches/:batchId): per-target Start/Resume/View cards, progress bar, 5s polling while in-progress, completion outcome summary
- Add BatchStatusCard: handles not-started/in-progress/complete states with step progress for in-progress targets
- Add ActiveBatchBanner: amber banner on detail page when a batch is running, links to BatchStatusPage
- Add MaintenanceContextStrip: amber strip in ProceduralNavigationPage for maintenance flows showing target name, batch progress (X/Y complete), and Back to Batch nav
- Update MaintenanceFlowDetailPage: active batch banner, clickable run history rows with mini progress dots and outcome summaries, Run button loading state, post-launch navigates to BatchStatusPage
- Update ProceduralNavigationPage: renders MaintenanceContextStrip between top bar and content when tree_type === 'maintenance'; fetches batch progress once on mount
- Add batch_id filter to GET /sessions backend endpoint and SessionListParams frontend type
- Add /flows/:id/batches/:batchId route to router

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/sessions.py

@@ -38,6 +38,7 @@ async def list_sessions(
     client_name: Optional[str] = Query(None, description="Search by client name (partial match)"),
     tree_name: Optional[str] = Query(None, description="Filter by tree name from snapshot"),
     tree_id: Optional[UUID] = Query(None, description="Filter by tree ID"),
+    batch_id: Optional[UUID] = Query(None, description="Filter by batch ID (maintenance batch runs)"),
     started_after: Optional[datetime] = Query(None, description="Filter sessions started after this datetime"),
     started_before: Optional[datetime] = Query(None, description="Filter sessions started before this datetime"),
     completed_after: Optional[datetime] = Query(None, description="Filter sessions completed after this datetime"),
@@ -73,6 +74,10 @@ async def list_sessions(
     if tree_id:
         query = query.where(Session.tree_id == tree_id)
 
+    # Batch ID filter
+    if batch_id:
+        query = query.where(Session.batch_id == batch_id)
+
     # Date range filters
     if started_after:
         query = query.where(Session.started_at >= started_after)