Fixture compatibility update.
- Fixture schema 2 adds the standards-form OPC root office-document relationship to every generated package.
- The public fact contract and twelve cases are retained; v0.1.0 artifacts remain immutable.
- Every baseline/candidate package now loads with the independent python-pptx reader, in addition to PCAB validation and the SlideFence reference adapter.
PCAB remains static-only: it does not open PowerPoint, follow targets, execute macros, activate OLE, or claim runtime behavior.