chore: update workspace state and memory

- Update workspace state timestamp
- Add weekly summary to MEMORY.md (removing duplicate entry)

HEARTBEAT.md

@@ -0,0 +1,18 @@
+# HEARTBEAT.md — Development Environment Checks
+
+## Active Heartbeat Task (2026-03-15)
+
+Run `/opt/aitbc/dev/scripts/dev_heartbeat.py` on each heartbeat and send its output as your reply.
+
+**Interpretation:**
+- If the script exits 0 → reply `HEARTBEAT_OK` (quiet, all well).
+- If the script exits 1 → paste its full markdown report and highlight issues.
+- If the script fails to execute → report the error and suggest manual checks.
+
+**Rationale:** This script checks:
+- Uncommitted Git changes
+- Build/test health (syntax, test discovery)
+- Recent log errors/warnings (last hour)
+- Outdated Poetry dependencies
+
+Helps keep the dev workspace healthy between cron jobs.