codeSplitters scale: move file search out of D1, per repo #626

Scale sideboard cards Search keeps every file and D1's 10 GB cap.

file_search (FTS5 in D1) holds the full text of every file's last commit, and its index adds space on top of that. Big digs use up D1's 10 GB.

Next step: FTS5 per repo in a repo coordinator DO for in-repo search; AI Search or Vectorize (or a fan-out) for search across repos.