Query optimization (dspy):
- Replace UNION ALL + sort with two parallel queries (asyncio.gather)
that each use (userid, use_time) composite index
- Python-side merge-sort of two pre-sorted sequences O(n)
- Concurrent FileStorage reads for ioinfo (asyncio.gather)
Indexes (models/*.json + /tmp/llmage_history_indexes.sql):
- llmusage: add idx_llmusage_userid_usetime (userid, use_time)
- llmusage_history: add idx_lh_userid_usetime (userid, use_time)
(was missing userid index entirely - main bottleneck)
