Changes

Fix Jenkins pipeline validation and database checks

Changes:
- Add dummy environment variables for docker-compose validation
- Change "Initialize Database" to "Verify Database" stage
- Update database verification to check existence instead of creating
- Add clear error messages if database/user don't exist
- Add authentik-postgres-host and authentik-postgres-port to credentials list

The database and user should be created manually using the Python script
before running the Jenkins pipeline.

Update documentation for manual database creation

Changes:
- Update pipeline stages list to reflect database verification
- Add prerequisites for Jenkins deployment
- Add note about create_db_user.py script
- Update CLAUDE.md to reflect manual database creation
- Clarify that Jenkins verifies database existence, doesn't create it