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/ProjectsController.cs

@@ -1,9 +1,11 @@
+using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Nexus.Api.DTOs;
 using Nexus.Api.Services;
 
 namespace Nexus.Api.Controllers;
 
+[Authorize]
 [ApiController]
 [Route("api/v1/projects")]
 public class ProjectsController(IProjectService projectService) : ControllerBase