When a user deletes an API token that was migrated from .env, track
the hash in a suppression list to prevent it from being re-migrated
on the next restart.
Changes:
- Add SuppressedEnvMigrations field to Config
- Add env_token_suppressions.json persistence
- Check suppression list during env token migration
- Record suppressed hash when deleting "Migrated from .env" tokens
- Update RemoveAPIToken to return the removed record
Related to #871