Track heartbeat/skills settings, add vault backup script

Settings that were silently lost on reinstall:
- Track .smallclaw/heartbeat/config.json (active hours 8-22, interval 30m)
- Track .smallclaw/skills_state.json (multi-agent-orchestrator enabled)
- Fix gitignore: heartbeat/ → heartbeat/runs/ (only ignore run logs, not config)
- Fix gitignore: remove skills_state.json from ignored list

Vault (contains channel tokens, passwords) cannot go in git — instead:
- Add scripts/backup-vault.sh: backs up vault+credentials to ~/.smallclaw-backup/
  keeping last 5 snapshots. Run manually or via cron (0 3 * * *).
- Run initial backup now → ~/.smallclaw-backup/vault_20260518_232441

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -44,11 +44,10 @@
 .smallclaw/tasks/
 .smallclaw/jobs/
 .smallclaw/ocr-cache/
-.smallclaw/heartbeat/
+.smallclaw/heartbeat/runs/
 .smallclaw/task-heartbeat.json
 .smallclaw/cron/runs/
 .smallclaw/skills/
-.smallclaw/skills_state.json
 .smallclaw/workspace_state.json
 .smallclaw/.migrated-from-localclaw