Move thread-list SQLite reads off the serving loop

[Guitaraholic]

Human comments

What was wrong

better-sqlite3 runs on the Node serving loop. One cold query on a 1.7GB bb.db froze every client for 11s, including WebSocket token streams (#1131).

What changed

• File-backed servers start one readonly WAL worker.
• Thread list and sidebar project+thread reads go through it (listThreadsWithPendingInteractionStateOffThread and the project-scoped variant).
• :memory: tests and a worker that fails to start keep the existing sync path.
• Bundled servers also emit dist/sqlite-read-worker.js.
• Search and timeline reads stay on the serving connection. No protocol change.

How you verified

• Added packages/db/test/sqlite-read-queue.test.ts: in-memory stays on the calling connection; a file-backed worker returns the same thread list as the serving connection.
• Desktop and app query tests for the other harvests passed in this checkout. Local db vitest workers OOM in this environment; CI should run the new file.

Fixes #1131

AGENT GENERATED