feat: schema change PR comment

[Xetera]

This should include the schema change in the PR comment. I expect this to not be a perfect PR because change detection can come up with wild diffs in schema for relatively simple changes. But at the minimum it should let the author (and agents) know that they've made some schema changes in the PR

[github-actions]

Query Doctor Analysis

3 queries analyzed

2 pre-existing issues

• SELECT "guests"."id", "guests"."session_id", "guests"."username", "guests"."avatar_path", "guests"."color", "guests"."side", "guests"."audio_recording_path", "guests"."audio_recording_public", "gue...
  index assets(event_id, inserted_at desc)
  cost 31,003,449 → 1,498 (100% reduction)
• SELECT * FROM guest_ip_addresses WHERE ip_address = '127.0.0.1';
  index guest_ip_addresses(ip_address)
  cost 154,402 → 8 (100% reduction)

_{Using assumed statistics (10000000 rows/table). For better results, sync production stats.}