Add heartbeat checks: email (2-3x daily), skills (weekly)

HEARTBEAT.md

@@ -1,4 +1,11 @@
 # HEARTBEAT.md
 
-# Keep this file empty (or with only comments) to skip heartbeat API calls.
-# Add tasks below when you want the agent to check something periodically.
+## Periodic Checks
+
+### Email (2-3x daily)
+Check `gmail unread` for new messages in hammer7839283@gmail.com.
+If new mail from Donovan (forwarded), read and summarize or take action.
+Track last check in `memory/heartbeat-state.json`.
+
+### Skills (weekly)
+Check clawdhub for new useful skills.