chore: fix migration collision, orphan index, and AUDIT typo on develop

[AlexMakesC0de]

Cleans up three issues that landed on develop via #40, before they bite anyone.

Changes

1. Duplicate migration number. develop had two 009 migrations (009_activity_notifications_realtime.sql and 009_fix_item_photos_upload_scoping.sql). Renamed the upload-scoping one to 010_fix_item_photos_upload_scoping.sql so ordering is unambiguous. 011 is unchanged.
2. Orphan index in init.sql. Improved quality #40 dropped the account_authentication table but left CREATE INDEX ... ON account_authentication at line 153, so a fresh init.sql run failed with "relation does not exist". Removed that line.
3. AUDIT.md header typo. A stray link was pasted into the word "Severity". Fixed, and updated the upload-scoping migration references from 009 to 010 to match the rename.

Notes

No code or schema behavior changes. The renamed migration file content is identical. The activity-notifications 009 migration is intentionally left as-is. Separately, still open from the #40 review: migration 011 (server-side purchase fee trigger) is written but not yet confirmed applied to the hosted project.

[NickGrahovskis]

The fixes for sql files are redunant bcs we will delete them, so only add changes to audit.md. If you want you can also delete the whole db folder, because it was only needed for local supabase which we are not using anymore