feat: Gateway health monitoring (Hermes CLI, API, frontend)

- Hermes CLI wrapper using subprocess.run for gateway status
- Gateway API: status list (with filter), events (placeholder), start/stop/restart with audit logging
- Frontend GatewayPage: timeline, filter bar, status table with 10s polling, operation modals
- usePolling hook for periodic data refresh

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

backend/app/main.py

@@ -4,7 +4,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.database import engine, Base
-from app.api import auth, users, audit, dashboard
+from app.api import auth, users, audit, dashboard, gateway
 from app.middleware.audit import AuditMiddleware
 
 
@@ -35,6 +35,7 @@ app.include_router(auth.router)
 app.include_router(users.router)
 app.include_router(audit.router)
 app.include_router(dashboard.router, prefix="/api/v1")
+app.include_router(gateway.router, prefix="/api/v1")
 
 
 @app.get("/api/v1/health")