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/Services/AgentService.cs

@@ -73,6 +73,7 @@ public interface IAgentService
 {
     Task<IReadOnlyCollection<AgentInfo>> GetAgentsAsync(CancellationToken cancellationToken);
     Task<AgentDetail?> GetAgentAsync(string id, CancellationToken cancellationToken);
+    Task<IReadOnlySet<string>> GetAllowedAgentIdsAsync(CancellationToken cancellationToken);
 }
 
 public sealed class AgentService(IConfiguration configuration, IAgentRuntime runtime) : IAgentService
@@ -151,6 +152,16 @@ public sealed class AgentService(IConfiguration configuration, IAgentRuntime run
         );
     }
 
+
+    public async Task<IReadOnlySet<string>> GetAllowedAgentIdsAsync(CancellationToken cancellationToken)
+    {
+        var configs = await LoadAgentConfigsAsync(cancellationToken);
+        return configs
+            .Where(config => !string.IsNullOrWhiteSpace(config.Id))
+            .Select(config => config.Id.Trim().ToLowerInvariant())
+            .ToHashSet(StringComparer.OrdinalIgnoreCase);
+    }
+
     private static string DeriveRole(string agentId) => agentId.ToLowerInvariant() switch
     {
         "iris" => "Orchestrator",