fix(store): sanitize FTS5 operators in buildFtsQuery (fixes #160)

[MLYoshi]

Summary

Closes #160

Adds FTS5 operator injection protection to buildFtsQuery() in src/core/store/sqlite.ts using a defense-in-depth approach:

Changes

src/core/store/sqlite.ts — New sanitizeFtsRaw() + token-level filter:

Layer	Purpose
Input-level (sanitizeFtsRaw)	Strip FTS5 syntax chars ("'()*:\^-) and boolean operators (AND/OR/NOT/NEAR) before tokenization. Uses \b word-boundary to protect words like ANDROID.
Token-level (FTS5_OPERATORS Set)	Secondary defense — filters operator tokens that may leak through jieba tokenizer.
Quoting	Filter empty tokens after replaceAll('"', "") to avoid bare "" in output.

All 4 existing call sites (auto-recall, l1-dedup, conversation-search, memory-search) benefit automatically with no changes needed.

src/core/store/sqlite.test.ts — 11 new security test cases covering:

• FTS5 boolean operators stripped (AND/OR/NOT/NEAR)
• Case-insensitive operator stripping
• FTS5 special characters ("'()*:\^-)
• Exclude operator (-) stripped
• Column filter syntax (content:foo) blocked
• Word-boundary protection (ANDROID preserved)
• Pure-operator input returns null
• Empty token filtering
• Jieba mock path sanitization
• Normal Chinese/English recall unaffected
• Empty/whitespace input

Testing

npx vitest run --reporter=verbose
# 5 files passed · 78 tests passed (67 existing + 11 new, zero regressions)

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