fix(db): graceful FTS5 fallback when Node.js build lacks FTS5 (#1532) (#1810)

* fix(db): graceful FTS5 fallback when Node.js build lacks FTS5 support (#1532)

Official Node.js binaries do not compile FTS5 by default, causing codegraph
init to fail with 'no such module: fts5'. Added runtime FTS5 detection:
- Split schema execution to try FTS5 separately, skip on failure with warning
- Added fts5Available flag to DatabaseConnection and QueryBuilder
- Bulk-load and search paths skip FTS5 operations when unavailable
- Search falls back to LIKE + fuzzy matching when FTS5 is missing

(cherry picked from commit ed708b7f60540367d8a810b0388aaa05ce0a0933)

* fix(db): preserve core schema during FTS5 fallback (#1532)

Keep required tables and indexes after the FTS triggers outside the
optional schema block in the upstream #1625 fix. Without this boundary,
simulated-missing-FTS5 indexing still fails on name_segment_vocab.

Add seven regressions using real SQLite with FTS5 creation intercepted,
covering initialization/open, LIKE and fuzzy search, non-FTS schema parity,
bulk no-ops, and real FTS5 search and bulk-load recovery. Credit
@aniruddhaadak80 under Unreleased fixes.

Validation on Linux x64 with Node v22.19.0:
- npm run build passed, including viewer and grammar asset checks.
- 34 tests passed across fts5-fallback, node-sqlite-backend,
  sqlite-backend, and db-perf.
- Rebuilt CodeGraph initialization, indexing, reopening, search, and
  cross-file callers passed with simulated missing FTS5 and real FTS5.

Fixes #1532.
Supersedes #1625.

---------

Co-authored-by: Aniruddha Adak <aniruddhaadak80@users.noreply.github.com>
Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>

CHANGELOG.md

@@ -140,6 +140,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 #### MCP / indexing
 
+- Indexing now succeeds when Node.js's SQLite lacks FTS5, with search falling back to name and fuzzy matching; thanks @aniruddhaadak80. (#1532)
+
 - `codegraph_explore` now makes clear that suggested call counts are advisory, so agents keep exploring when an answer is incomplete; thanks @rongbc. (#1504, #1570)
 
 - C++ functions following anonymous namespaces containing raw-string templates are now indexed correctly, even when template text resembles an unfinished macro call. (#1505)