feat(systemd): Dashboard-Service, brain_rules, 18 Engramme bewertet, Cron persistent

Neu:
- systemd: secondbrain-dashboard.service (Port 8501, autostart)
- cron_rules.py: Auto-Confirm ab 3x, Archiv nach 30d
- cron_tasks/: heartbeat + backup + brain_rules (persistent)
- openclaw_cron_wrapper.py: subprocess-Isolation (kein SessionTakeover)
- chat_autosave.py: Auto-Save von Chat + Kontext-Anreicherung

Daten:
- 18 unbestätigte Engramme bewertet:
  - 14x CONFIRMED (Fakten/Definitionen korrekt)
  - 3x ARCHIVIERT (historisch, nicht aktuell)
  - 1x CONFIRMED (Regel 73624013)
- 0 offene unbestätigte

Closes Gitea-Issue: #9

cron_tasks/backup_secondbrain.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+"""Backup-Task für Second Brain - isoliert, persistent."""
+import json, os, sys
+from pathlib import Path
+from datetime import datetime, timezone
+
+BRAIN_DIR = Path("/root/.openclaw/workspace/second-brain")
+sys.path.insert(0, str(BRAIN_DIR))
+from src.store import EngramStore
+
+def main():
+    brain_db = os.environ.get("BRAIN_DB", str(BRAIN_DIR / "data" / "brain.sqlite"))
+    store = EngramStore(brain_db)
+    ts = datetime.now(timezone.utc).strftime("%Y%m%d_%H%M%S")
+    backup_path = Path(brain_db).parent / f"backup_{ts}.jsonl"
+    count = store.export_jsonl(str(backup_path))
+    result = {"timestamp": datetime.now(timezone.utc).isoformat(), "backup_path": str(backup_path), "count": count, "success": True}
+    print(f"BACKUP: {count} Engramme -> {backup_path}")
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(main())