Threads the strict BuildingPartIdentifier type (introduced in a8b443f6)
through the two remaining backend touchpoints:
- EpcBuildingPartModel.from_*: SQLModel column expects a string, so
unbox the enum with .identifier.value before binding to the DB.
- documents_parser end-to-end tests: swap bare-string equality
("main" / "extension_1") for identity checks against the enum
members (BuildingPartIdentifier.MAIN / EXTENSION_1).
Documents_parser test pack passes (105/105). No dedicated SQLModel test
covers EpcBuildingPartModel.from_*; the .value line is exercised
transitively via db_writer.py / local_runner.py in production.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
