Add multilingual scriptgram search

[luca-ctx]

Summary

• add scriptgram FTS sidecar tables for scripts that default SQLite FTS tokenizes poorly
• merge scriptgram hits with normal record/event FTS only for covered non-Latin queries
• add v45 migration/backfill plus multilingual regression coverage

Impact

English/code-only text and queries stay on the existing FTS path and do not populate the sidecar. Multilingual rows get additional sidecar tokens for Japanese, Chinese, Korean, Thai/Lao/Khmer/Myanmar, and major Indic scripts.

Validation

• cargo test -p ctx-history-store
• cargo test -p ctx-history-search
• cargo test --workspace
• dogfooded real ctx import/search against ctx-history-jsonl-v1 fixture for 認証, OAuth 認証, 登录态, 오류, and SearchResultScope