Critical fixes:
1. LIKE ESCAPE '\' clause added for namePrefix queries
2. list() limit/offset now applied AFTER tag/label post-filter
3. tag()/untag() wrapped in db.transaction()
Warning fixes:
4. set()/update() wrapped in db.transaction() (txnSetVar)
5. listByTag sort/limit/offset pushed to SQL
6. close() idempotent (double-close guard)
7. JSONL → SQLite migration on first open (vars + tags)
8. History truncation simplified (NOT IN subquery)
9. Removed unnecessary pre-fetch in upsert (ON CONFLICT handles it)
Nits:
10. Database.Database type instead of InstanceType
11. row.name instead of row["name"]
12. DESC index on var_history position
13. key+value composite index on tags