fix(store): keep combining marks inside FTS5 tokens

[costajohnt]

Fixes #966

FTS5_SEPARATOR_RUN in src/store.ts splits query terms on anything that is not a letter, number, apostrophe or underscore. Combining marks (\p{M}) fall outside that class, so a decomposed (NFD) word such as impôt (o + U+0302) was split into impo and t, the query became "impo t", and FTS5 returned nothing. This started with #939.

The change adds \p{M} to the character class, so marks stay inside the token; sanitizeFTS5Term then drops the mark as before, and precomposed input is unaffected.

Tests: new cases in test/store-fts-separator-queries.test.ts for NFD impôt and café staying one token and matching; they fail on main. 23 pass under both bun test and vitest, bun run lint clean. CHANGELOG entry under Unreleased.