feat: push OpenClaw metadata to Monitor bridge periodically

- MonitorBridgeClient gains pushOpenClawMeta() method for POST /openclaw
- OpenClawMeta interface defines version/plugin_version/agents payload
- Plugin pushes metadata on gateway_start (delayed 2s) and periodically
- Interval aligns with reportIntervalSec (default 30s)
- Pushes are non-fatal — plugin continues if Monitor is unreachable
- Interval cleanup on gateway_stop
- Updated monitor-server-connector-plan.md with new architecture

docs/monitor-server-connector-plan.md

@@ -2,46 +2,53 @@
 
 ## Current design
 
-The plugin uses:
+The plugin and Monitor communicate over a local bridge port (`monitor_port` / `MONITOR_PORT`).
 
-- **HTTP heartbeat** to `/monitor/server/heartbeat-v2`
-- **API Key authentication** via `X-API-Key`
-- **Gateway lifecycle hooks**: `gateway_start` / `gateway_stop`
+### Data flow
+
+1. **Monitor → Plugin** (GET): Plugin queries `GET /telemetry` on the bridge for host hardware data.
+2. **Plugin → Monitor** (POST): Plugin pushes OpenClaw metadata via `POST /openclaw` to the bridge.
+3. **Monitor → Backend**: Monitor heartbeats to `POST /monitor/server/heartbeat-v2` with `X-API-Key`, enriched with any available OpenClaw metadata.
+
+### Bridge endpoints (on Monitor, 127.0.0.1:MONITOR_PORT)
+
+| Endpoint | Method | Description |
+|----------|--------|-------------|
+| `/health` | GET | Health check, returns monitor version and identifier |
+| `/telemetry` | GET | Latest hardware telemetry snapshot |
+| `/openclaw` | POST | Receive OpenClaw metadata from plugin |
+
+### Plugin behavior
+
+- On `gateway_start`, plugin begins periodic metadata push (aligned with `reportIntervalSec`).
+- Initial push is delayed 2s to allow Monitor bridge startup.
+- If bridge is unreachable, pushes fail silently. Plugin remains fully functional.
+- On `gateway_stop`, periodic push is stopped.
 
 ## No longer used
 
 The following design has been retired:
 
-- challenge UUID
-- RSA public key fetch
-- encrypted handshake payload
-- WebSocket telemetry
+- challenge UUID / RSA handshake / WebSocket telemetry
+- Plugin-side `server/` sidecar process
 
-## Runtime flow
-
-1. Gateway loads `harborforge-monitor`
-2. Plugin reads config from OpenClaw plugin config
-3. On `gateway_start`, plugin launches `server/telemetry.mjs`
-4. Sidecar collects:
-   - system metrics
-   - OpenClaw version
-   - plugin version
-   - configured agents
-5. Sidecar posts telemetry to backend with `X-API-Key`
-
-## Payload
+## Heartbeat payload
 
 ```json
 {
   "identifier": "vps.t1",
   "openclaw_version": "OpenClaw 2026.3.13 (61d171a)",
-  "plugin_version": "0.1.0",
+  "plugin_version": "0.2.0",
   "agents": [],
   "cpu_pct": 10.5,
   "mem_pct": 52.1,
   "disk_pct": 81.0,
   "swap_pct": 0.0,
   "load_avg": [0.12, 0.09, 0.03],
-  "uptime_seconds": 12345
+  "uptime_seconds": 12345,
+  "nginx_installed": true,
+  "nginx_sites": ["default"]
 }
 ```
+
+`openclaw_version`, `plugin_version`, and `agents` are optional enrichment from the plugin. If plugin never pushes metadata, these fields are omitted and the heartbeat contains only hardware telemetry.