Gateway: add healthz/readyz probe endpoints for container checks (#31272)

* Gateway: add HTTP liveness/readiness probe routes

* Gateway tests: cover probe route auth bypass and methods

* Docker Compose: add gateway /healthz healthcheck

* Docs: document Docker probe endpoints

* Dockerfile: note built-in probe endpoints

* Gateway: make probe routes fallback-only to avoid shadowing

* Gateway tests: verify probe paths do not shadow plugin routes

* Changelog: note gateway container probe endpoints

docker-compose.yml

@@ -26,6 +26,18 @@ services:
         "--port",
         "18789",
       ]
+    healthcheck:
+      test:
+        [
+          "CMD",
+          "node",
+          "-e",
+          "fetch('http://127.0.0.1:18789/healthz').then((r)=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))",
+        ]
+      interval: 30s
+      timeout: 5s
+      retries: 5
+      start_period: 20s
 
   openclaw-cli:
     image: ${OPENCLAW_IMAGE:-openclaw:local}