Implement database migration tooling with rollback support

[Smartdevs17]

Description

Database schema changes are applied manually without versioning or rollback capability. Implement automated migration tooling with up/down migrations and CI validation.

Acceptance Criteria

• Migration framework (db-migrate or Prisma Migrate)
• Up/down migration files with versioning
• Migration status tracking in database
• Automatic migration on deployment
• Rollback command for failed deployments
• CI check for migration conflicts

Technical Scope

• backend/migrations/
• backend/src/config/database.ts
• .github/workflows/
• Edge: long-running migrations, zero-downtime migration strategies, concurrent migration prevention