fix: performance optimizations for large dataset

- Add generated columns and indexes for correctness and metadata fields
- Optimize get_all() with keyset pagination
- Add get_pending_for_review() for targeted queries
- Update cron tasks to use optimized queries instead of full table scans
- This fixes timeouts in review_brain and verify_pending_external (300s timeout)

Fixes #35: Second-Brain in Takt bringen, Dedup, Pendings, Graph und Performance

systemd/openclaw-secondbrain-ingest-memory.path

@@ -4,6 +4,8 @@ PartOf=openclaw-secondbrain.target
 
 [Path]
 PathModified=/root/.openclaw/workspace/memory
+TriggerLimitIntervalSec=60
+TriggerLimitBurst=3
 
 [Install]
-WantedBy=multi-user.target
+WantedBy=default.target