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

frontend/src/stores/tasks.ts

@@ -359,8 +359,12 @@ export const useTaskStore = defineStore('tasks', {
       }
     },
 
-    startBoardPolling() {
-      if (this.boardRefreshInterval) return
+    startBoardPolling(force = false) {
+      if (this.boardRefreshInterval && !force) return
+      if (this.boardRefreshInterval && force) {
+        clearInterval(this.boardRefreshInterval)
+        this.boardRefreshInterval = null
+      }
       this.fetchBoard()
       this.boardRefreshInterval = setInterval(() => {
         this.fetchBoard()