fix: add /health endpoint for health checks

Add simple health check endpoint that returns {status: healthy}.
Needed for Traefik health checks and monitoring.

apps/api/src/main.py

@@ -86,6 +86,10 @@ services:
 async def on_startup():
     await seed_builtin_tool_types()
 
+@app.get("/health")
+async def health_check():
+    return {"status": "healthy"}
+
 app.include_router(auth_router)
 app.include_router(projects_router)
 app.include_router(users_router)