feat: Cron management API and frontend page (Phase 5)

Backend: CRON API with list/logs/run/pause/resume endpoints, Hermes CLI
integration, system cron jobs, audit logging for operations.
Frontend: CronPage with filter bar (status/profile), table with 30s polling,
log modal with level-colored messages, action buttons (run/pause/resume),
run confirmation dialog, 4-state coverage. Sidebar shows cron failure badge.

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, gateway, health
+from app.api import auth, users, audit, dashboard, gateway, health, cron
 from app.middleware.audit import AuditMiddleware
 
 
@@ -37,6 +37,7 @@ app.include_router(audit.router)
 app.include_router(dashboard.router, prefix="/api/v1")
 app.include_router(gateway.router, prefix="/api/v1")
 app.include_router(health.router, prefix="/api/v1")
+app.include_router(cron.router, prefix="/api/v1")
 
 
 @app.get("/api/v1/health")