Township: dedicated keyframes page for a match + outcome fixes

- New /match/keyframes page (🖼 Keyframes ▸ from the match page): thumbnail
  grid of every clip + planned-outcome keyframe, each with per-tile
  regenerate (image model) and delete, plus match-level Regenerate all /
  Clear all. Live progress bars; reloads on completion with mtime
  cache-bust.
- Regenerate all (whole match) now also covers this match's OUTCOME
  keyframes, not just clips.
- Clear all now removes planned outcome keyframes too (not only ones with a
  rendered video), keeping it symmetric with Regenerate all.
- Fix outcome keyframe stem on the page: use the plan entry's actual
  match_name (None → legacy "<fighter>_<outcome>") so it matches the file
  the generator writes, instead of a "<match>_<fighter>_<outcome>" that is
  never created (outcome keyframes were showing "no keyframe" after a
  successful regen).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>