codeSplitters scale: search across repos without the fan-out (AI Search or Vectorize) #636

Since #626, search in one repo is one Durable Object, and search across repos fans out to at most 50 repos you can see (yours first, then the most recently committed), merging by bm25 rank. Repos past those 50 are missed, and ranks from separate indexes only roughly compare.

Next step: an index across repos (Cloudflare AI Search or Vectorize) that the commit path also feeds, filtered by what the caller can see. The scale sideboard's search card names this.