chore(#4024): drop stray .review-crops/ scratch from the release diff

The release diff committed 7 PNG review-crop screenshots under a root-level
.review-crops/ directory (652K) that nothing references — not the CHANGELOG,
docs HTML, or any source file. These are deep-review before/after scratch
shots, not durable UX evidence (the intended evidence lives in
docs/ui-ux/evidence/pr4024-*.png and is kept). Shipping them in v0.51.375
would bloat the repo history permanently for every user.

Remove the directory and add .review-crops/ to .gitignore (next to the
.local-review/ harness entry) so review scratch can't leak into a release
diff again — mirroring the stray-uv.lock drop in #3963.

No code or test change; the Transparent Stream feature is untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -59,6 +59,7 @@ EXECUTION_LOG.md
 # Local-only PR review harness: rendering drivers, sample bank, fixtures.
 # Used by Claude during deep reviews; never shared in the repo.
 .local-review/
+.review-crops/
 graphify-out/
 .graphify_cached.json
 .graphify_uncached.txt