Group generated-output differences by test case

[schani]

Change

Group generated files by their input test case instead of listing them in target-first path order.

Each test group now shows:

• the input test path;
• the number of affected generated files;
• aggregate insertions/deletions; and
• files sorted by target, with the target called out separately from the renderer options/output path.

Search and target/status filters hide empty test groups, and the summary includes the number of affected test cases.

Live example

The existing #2983 report has been explicitly regenerated with this renderer. Its 95 generated files are now organized into the 3 actual affected test cases:

https://hostr.flingit.run/s/quicktype/output-diffs/pr-2983/4a414e28a17dfcad70829842b5cc016090602b27/444607b9d6138ea753ec0c50dcba1ce5bdb1054f/index.html

Verification

• Focused report tests pass.
• TypeScript typecheck passes.
• Biome lint and git diff --check pass.
• The regenerated report contains exactly 3 test groups and all 95 generated files; the uploaded content hash matches the local render.

[github-actions]

No generated-output differences

✅ This PR does not change generated outputs.