Spawning a full openclaw CLI process every 30s to list agents is too
heavy — each invocation loads all plugins (~16s) and hangs until killed.
Return empty array for now until a lighter mechanism is available.
api.version returns plugin API version (0.2.0), not the openclaw release
version. Use OPENCLAW_SERVICE_VERSION env var set by the gateway instead.
Also increase listOpenClawAgents timeout from 15s to 30s since plugin
loading takes ~16s on T2.