v8.yaml: annotate each bug with classification + fix-commit subject

Cosmetic comment-only change; YAML parses to an identical dict before
and after.

- Adds a (subsystem, jit, sbx_bypass, year) annotation comment above
  each env entry.
- Replaces the ad-hoc trailing comments on each `- id:` line with the
  actual fix-commit Subject line for that bug.
- Drops a legacy heuristic comment block about subsystem labelling.

Bug ordering, env IDs, image refs, seeds, and budgets are unchanged.