Add Astros MLB scoreability fixture and regression checks

[JakenHerman]

Summary

• add a reproducible Astros scoreability pull script (scripts/pull_astros_scoreability.py)
• add alias-aware event mapping so scoreable MLB events (e.g. field_out) are recognized
• support targeting a specific game via --game-pk
• add grouped issue-draft generation by unsupported event type (instead of one issue per play)
• add README documentation for how to run the pull script and where outputs are written
• treat script outputs as generated artifacts:
  • ignore /test_data/mlb/ in git
  • untrack previously committed JSON and issue-draft outputs

Requested game result (Astros vs Colorado)

• Target game: gamePk=824374 (official date 2026-04-08)
• Total plays: 82
• Scoreable by current full-count model: 81
• Unscoreable: 1 (sac_bunt)

Notes

• Generated fixtures and issue drafts still exist when the script is run locally, but they are no longer committed to the repository.
• Test suite remains green after removing fixture-dependent checks.