fix(gh-monitor): replace OpenClaw cron with launchd — zero polling token cost

gh-monitor/design.md

@@ -115,16 +115,16 @@ intervals across a handful of repos, this is nowhere near the limit.
 
 ---
 
-## Cron Schedule
+## Schedule
 
-Every 5 minutes via OpenClaw cron:
-```
-{ "kind": "every", "everyMs": 300000 }
-```
+Every 5 minutes via macOS `launchd` (LaunchAgent plist). `poll.py` runs as a
+plain shell process — no agent session, no tokens consumed during polling.
 
-Payload: systemEvent → injects wake text into main session.
+The main session is only woken when `poll.py` finds new activity and calls
+`openclaw system event`. On a quiet repo this costs zero tokens most of the day.
 
-Can be paused/resumed via OpenClaw cron management without touching the code.
+The LaunchAgent can be unloaded/loaded via `launchctl` to pause/resume polling
+without touching the code.
 
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