[plan-25] Search Read Path (FTS/CJK) — CJK-aware matching when FTS5 unicode61 returns 0

## Defect FTS5 unicode61 can't segment CJK → phrase search always returns 0 even when rows exist. Chroma-empty→FTS fallback does not fix matching. ## Children - #3801 - #3859 ## Related PRs - #3810 - #3173 - #3285 - #3430 ## Fix sequence CJK-aware tokenizer / trigram / LIKE fallback on script detect; same contract on worker SQLite and server search. ## Test matrix - CJK query × worker SQLite FTS × server search - Empty-chroma fallback path ## Out of scope - Chroma spawn/pin (plan-22 #3610) - Project identity (plan-20)