fix: untrack output/replays/bomber_replay_*.jsonl (was committed despite gitignore)

output/ has been in .gitignore since line 4, but this replay file was
accidentally committed at some point. The 'tracked AND ignored' state
causes release-plz to detect a dirty working directory in CI and refuse
to run:

  ERROR: the working directory of this project has uncommitted changes.
  If these files are both committed and in .gitignore, either delete
  them or remove them from .gitignore.
  ["output/replays/bomber_replay_1778583858.jsonl"]

Fix: git rm --cached (untrack, keep on disk). No .gitignore change
needed — output/ is already ignored. Verified no other ignored dirs
(.raw, checkpoints/, .logs) have tracked files.

Author: katopz