V72: Rename id → uuid on Category A tables + add missing FK constraints.

Category A tables have a UUID primary key column named id. Ecto schemas map field :uuid → DB column id via source: :id. This migration renames the DB column to uuid so the source: :id mapping is no longer needed.

Changes

• Rename id → uuid on 30 Category A tables (metadata-only, instant)
• Add 4 missing FK constraints:
  • phoenix_kit_comments.user_uuid → phoenix_kit_users.uuid (CASCADE)
  • phoenix_kit_comments_dislikes.user_uuid → phoenix_kit_users.uuid (CASCADE)
  • phoenix_kit_comments_likes.user_uuid → phoenix_kit_users.uuid (CASCADE)
  • phoenix_kit_scheduled_jobs.created_by_uuid → phoenix_kit_users.uuid (SET NULL)

All operations are idempotent (guarded by column/constraint existence checks).

Safety

• Column renames are metadata-only in PostgreSQL — zero downtime, instant
• 29 existing FK constraints referencing these columns auto-update on rename
• Deploy is atomic: migration runs on startup before new code serves traffic