QuickBook round-trip translation

[whisper67265]

Problem

No integration test exercises the full QuickBook translation round-trip: creating a project and component via the Weblate REST API with a QBK fixture, verifying units are extracted, and downloading the translated .qbk file.

Acceptance Criteria

• Test creates a project + component via Weblate REST API with a QBK fixture file
• Verifies translation units are extracted correctly
• Downloads translated .qbk file and verifies output structure
• Test runs as part of integration-functional.yml
• PR approved by at least 1 reviewer

References

• Related files: boost_weblate/formats/quickbook.py, test fixture .qbk file