Audit legacy enum type usages and prepare Alembic migration scripts

Goal
Audit legacy enum type usages and prepare DB migrations required for a safe transition to StrEnumType.

Scope
1. Audit current model/schema usages of legacy enum types
2. Analyze DB\-level impacts on enum types/values
3. Write Alembic migration script\(s\) and rollback strategy
4. Validate migration flow in test/staging environment

Definition of Done
\- Usage audit list is completed
\- Required Alembic migration script\(s\) are prepared
\- Forward/rollback paths are documented
\- Validation results are recorded

JIRA Issue: BA-4705