Add more real-world questions to the retrieval eval #5

Kitty's tutor is checked by a retrieval eval: 52 real-world Git questions, each with the source files that should come back in the top 6 results (hit@6). More questions = better answers, because every miss points at a gap we can fix.

What to do

1. Add 5–10 new questions to kitty/ingest/eval/questions.json. Write them the way a real person would ask (short, casual, even with typos), on topics that aren't covered yet, e.g. git tag, git worktree, .gitattributes, git clean, sparse checkout, git log filters, signing commits.
2. For each one, list the source files that answer it in expected (source names are in kitty/server/data/index.json, or run the eval with --verbose to see what comes back).
3. Run:

   cd kitty
   npm ci
   npm run eval -w ingest -- --verbose

4. Open a PR with the new questions. If one is a MISS, say so in the PR; finding a miss is a useful contribution too.

No API key is needed. The eval runs offline.