feat: board-first orchestration with Gateway Bridge, live-update, and flow-board

- GatewayBridgeController: MCP-artiger Kommando-Adapter für Agent-zu-Backend
- TaskBridgeService + LiveUpdateService: SSE Live-Sync + Bridge-Kommandos
- FlowBoard.vue: Board-first orchestration dashboard panel
- live-sync.ts store + live.ts service: SSE-basierte Live-Updates
- Nullability-Warnung in HealthController.cs gefixt
- nginx.conf: SSE-Proxy + CORS für Bridge-Endpunkte
- .gitignore: pnpm/corepack local caches ausgeschlossen
- docs: architecture-board-first-orchestration.md hinzugefügt
- README: Backend Bridge API dokumentiert

backend/Controllers/NotificationsController.cs

@@ -31,6 +31,16 @@ public class NotificationsController(INotificationService notificationService) :
         return Ok(new UnreadCountDto(count));
     }
 
+    [HttpGet("snapshot")]
+    public async Task<ActionResult<NotificationSnapshotDto>> GetSnapshot(
+        [FromQuery] string forUser = "bao",
+        [FromQuery] int limit = 50,
+        [FromQuery] bool unreadOnly = false,
+        CancellationToken ct = default)
+    {
+        return Ok(await notificationService.GetSnapshotAsync(forUser, limit, unreadOnly, ct));
+    }
+
     [HttpPatch("{id:guid}/read")]
     public async Task<ActionResult> MarkAsRead(Guid id, CancellationToken ct = default)
     {