feat: container monitoring backend core (PR-1)

- Add instance_events and health_checks tables with Alembic migration
- InstanceEventBus: typed pub/sub singleton with wildcard support
- HealthMonitor: async background loop polling containers every 15s
- SSE endpoint GET /events/stream with auth and connection limits
- Lifecycle hooks in tool_instances.py (create/start/stop/restart/delete)
- Structured JSON logging with correlation IDs
- 15 new unit tests (EventBus, HealthMonitor, MonitoringModels)

Quality gates: pytest 15 new passed, ruff clean

apps/api/src/main.py

@@ -9,6 +9,7 @@ from fastapi.staticfiles import StaticFiles
 
 from src.api.auth import router as auth_router
 from src.api.dashboard import router as dashboard_router
+from src.api.events import router as events_router
 from src.api.git_repositories import router as git_repositories_router
 from src.api.health import router as health_router
 from src.api.projects import router as projects_router
@@ -30,6 +31,9 @@ from src.logging_config import (
     RequestLoggingMiddleware,
     configure_logging,
 )
+from src.services.correlation import CorrelationIdMiddleware
+from src.services.event_bus import InstanceEventBus
+from src.services.health_monitor import HealthMonitor
 
 # Configure logging early
 log_level = os.getenv("LOG_LEVEL", "INFO").upper()
@@ -54,6 +58,7 @@ app.add_middleware(
     allow_headers=["*"],
 )
 
+app.add_middleware(CorrelationIdMiddleware)
 app.add_middleware(RequestLoggingMiddleware)
 app.add_middleware(ExceptionLoggingMiddleware)
 
@@ -103,6 +108,11 @@ async def validation_exception_handler(request: Request, exc: RequestValidationE
     )
 
 
+# Global services
+_event_bus = InstanceEventBus()
+_health_monitor = HealthMonitor(_event_bus)
+
+
 @app.on_event("startup")
 async def on_startup():
     logger.info("Starting up Headquarter API...")
@@ -115,9 +125,21 @@ async def on_startup():
 
         sys.exit(1)
 
+    # Start background health monitor
+    _health_monitor.start()
+    logger.info("Health monitor started")
+
     logger.info("Startup complete.")
 
 
+@app.on_event("shutdown")
+async def on_shutdown():
+    logger.info("Shutting down Headquarter API...")
+    _health_monitor.stop()
+    logger.info("Health monitor stopped")
+    logger.info("Shutdown complete.")
+
+
 app.include_router(health_router)
 app.include_router(auth_router)
 app.include_router(dashboard_router)
@@ -133,4 +155,5 @@ app.include_router(tool_instances_router)
 app.include_router(sessions_router)
 app.include_router(instance_proxy_router)
 app.include_router(terminal_router)
+app.include_router(events_router)
 app.mount("/uploads", StaticFiles(directory="uploads"), name="uploads")