feat(phase4): add gateway:startup hook for auto-starting watcher daemon

- hooks/status-watcher-hook/HOOK.md — events: ["gateway:startup"], required env vars
- hooks/status-watcher-hook/handler.js — checks PID file, spawns watcher-manager.js detached
- Deployed hook to /home/node/.openclaw/workspace/hooks/status-watcher-hook/
- make check passes

hooks/status-watcher-hook/HOOK.md

@@ -0,0 +1,53 @@
+# status-watcher-hook
+
+Auto-starts the Live Status v4 daemon when the OpenClaw gateway starts.
+
+## Events
+
+```json
+["gateway:startup"]
+```
+
+## Description
+
+On gateway startup, this hook checks whether the status-watcher daemon is already
+running (via PID file). If not, it spawns `watcher-manager.js start` as a detached
+background process, then exits immediately. The daemon continues running independently
+of this hook handler.
+
+## Required Environment Variables
+
+The following environment variables must be set for the watcher to function:
+
+```
+MM_TOKEN         Mattermost bot token
+MM_URL           Mattermost base URL (e.g. https://slack.solio.tech)
+TRANSCRIPT_DIR   Path to agent sessions directory
+SESSIONS_JSON    Path to sessions.json
+```
+
+Optional (defaults shown):
+
+```
+THROTTLE_MS               500
+IDLE_TIMEOUT_S            60
+MAX_STATUS_LINES          15
+MAX_ACTIVE_SESSIONS       20
+MAX_MESSAGE_CHARS         15000
+HEALTH_PORT               9090
+LOG_LEVEL                 info
+PID_FILE                  /tmp/status-watcher.pid
+CIRCUIT_BREAKER_THRESHOLD 5
+CIRCUIT_BREAKER_COOLDOWN_S 30
+```
+
+## Installation
+
+This hook is deployed automatically by `install.sh` or `deploy-to-agents.sh`.
+To deploy manually:
+
+```sh
+cp -r hooks/status-watcher-hook /home/node/.openclaw/workspace/hooks/
+```
+
+The hook activates on the next gateway startup.