shop/doc/custom-apps/specs.md

• manifest.yaml (name, version, depends_on, conflicts_with, required: false, provides)
• init.py (router: APIRouter, optional on_load() for event handlers / DI registration)
• models.py (optional, with own SQLAlchemy Base subclass)
• projector.py (optional, redis read-store sync via event handlers)
• migrations/ (optional, alembic version files discovered by core migrations orchestrator)
• i18n/ (optional, DE/EN strings)
• frontend components under frontend/shop and/or frontend/admin (optional)