perf(file-search): speed up path-like queries

[JustYannicc]

Summary

• Cache normalized tilde paths in the file-search index entries so path-like scans stop recomputing them per query.
• Use existing prefix buckets to choose the most selective safe path-token candidate set before exact path filtering.
• Add temp-directory correctness coverage plus an opt-in large synthetic performance harness for path-like queries.

Metrics

Harness: SUPERCMD_FILE_SEARCH_PERF=1 node scripts/test-file-search-index.mjs on a 61,201-entry synthetic temp-home index with 360 path-like queries.

• Before: 15,580.41 ms total, 43.279 ms/query.
• After: 17.89 ms total, 0.050 ms/query.

Validation

• node scripts/test-file-search-index.mjs
• SUPERCMD_FILE_SEARCH_PERF=1 node scripts/test-file-search-index.mjs
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm test
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run build:main
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run check:i18n
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run build:renderer
• Codex LSP diagnostics: src/main errors = 0

Notes

• check:i18n exits 0 and still reports existing missing Italian keys: settings.ai.whisper.vocabulary, settings.extensions.appSearchScope.
• build:renderer emits existing Vite CJS and stale Browserslist warnings.
• Direct push to origin was denied, so this PR uses the JustYannicc fork head branch.

[JustYannicc]

Superseded by the consolidated upstream PR #535: #535