Fix watchdog health checks under Tailscale Serve

[chrysb]

Summary

• switch watchdog health checks from the WS-backed openclaw health --json CLI path to the local HTTP /health endpoint
• add short timeouts to WS-backed node/device CLI reads so hung subprocesses do not pile up under gateway.tailscale.mode=serve
• stop repeated auto-repair and notification loops while a prior repair is still awaiting recovery

Testing

• npm test -- tests/server/watchdog.test.js tests/server/routes-nodes.test.js tests/server/routes-pairings.test.js

Closes #21