feat(ci): improve test failure comment formatting and UX
- Add test categorization by type (e2e/integration/dev/prod), bundler (turbopack/rspack/webpack), platform (linux/windows)
- Add staleness indicator when new tests are running
- Track tests that passed on retry (likely flaky)
- Detect tests failing across multiple open PRs
- Improve reproduction commands with grouping by test type
- Add summary table with commit/run info and re-run link
- Add footer with links to testing docs
