Add Alembic migration system for database schema versioning

- Introduced `alembic.ini` for Alembic configuration, enabling structured database migrations.
- Created `database/migrations/env.py` to manage migration environment and database URL retrieval.
- Added migration script template `database/migrations/script.py.mako` for generating migration scripts.
- Updated `.gitignore` to exclude migration versions from version control.
- Enhanced `setup.md` documentation to include details on the migration system and commands for managing migrations.

.gitignore

@@ -2,3 +2,4 @@
 .env
 .env.local
 .env.*
+database/migrations/versions/*