fix(runtime): watchdog canonical liveness

src/k1link/web/app.py

@@ -528,6 +528,17 @@ async def request_validation_error_handler(
     return JSONResponse(status_code=422, content={"detail": INVALID_REQUEST_DETAIL})
 
 
+@app.get("/api/liveness")
+async def liveness() -> dict[str, object]:
+    """Prove only that the canonical event loop is responsive."""
+
+    return {
+        "ok": True,
+        "status": "alive",
+        "service": "mission-core-control-plane",
+    }
+
+
 @app.get("/api/health")
 def health() -> dict[str, Any]:
     return build_runtime_readiness(