chore(format): stop prettier rewriting the generated eval baseline

[mrsibe]

Fixes the recurring uncommitted docs/eval noise.

The committed docs/eval/baseline-v1.4.json is the eval harness output verbatim — src/main/eval/run.ts writes it with JSON.stringify(report, null, 2) — which is deliberately not prettier's formatting. Prettier collapses the short matchesByRank arrays onto one line, turning a 12 KB file into an 8 KB one without changing a value.

So prettier was a second writer for a generated file. npm run format reformatted both files and left a dirty worktree behind: a ~450-line diff that said nothing, which then had to be manually excluded from every unrelated PR (it showed up in this session's work on #118, #120 and #122).

Both files are now ignored. docs/eval/baseline-* rather than the directory, so a hand-written document landing in docs/eval/ later is still formatted.

Why ignoring is the right fix rather than reformatting

Regenerating these is a documented command (npm run eval, which "rewrites docs/eval/" per CONTRIBUTING), and the baseline's entire value is that it is byte-comparable to what the harness produces — verify.yml diffs a fresh run against the committed file to prove the committed numbers still reproduce. Reformatting it once would have hidden the churn for exactly one commit and left the next npm run eval dirty again, because the harness would keep writing its own format.

Verification

• npx prettier --check . — no issues repo-wide (it previously flagged both baseline files)
• npx prettier --check --ignore-path /dev/null docs/eval/baseline-v1.4.json — still flagged, which is the point: the file is untouched, and the churn stops because it is left alone rather than reformatted once
• npm test 254 pass · npm run typecheck · npm run check:design · npm run lint 0 errors (107 warning baseline unchanged)
• The committed baseline bytes are unchanged in this PR, so the verify.yml determinism diff is unaffected

One file, 8 added lines.