Scheduled-loop infra: lockfile guard + release + fire log

- scripts/loop-guard.sh — atomic claim with 30-min staleness overtake,
  appends NDJSON event to .loop-logs/<lang>.ndjson. Exit 0 = go ahead,
  exit 1 = another run is live, skip.
- scripts/loop-release.sh — clear lock, log release with exit status.

Intended for 7 per-language /schedule routines firing every 15 minutes.
Lock detects overlap so tight cadences are safe; stale lock (>30 min)
overtaken automatically if an agent dies mid-run.

.gitignore

@@ -29,3 +29,7 @@ test-case-define.txt
 test_all.js
 test_final.js
 test_interactive.js
+
+# Loop lock/log state
+.loop-locks/
+.loop-logs/