docs: clarify MOSS speaker-label boundaries

[LauraGPT]

Summary

• describe MOSS S01 / S02 values as anonymous labels within one recording
• state explicitly that this is diarization, not known-person identification or enrolled voiceprint verification
• retain the OpenMOSS ownership, no-external-VAD, and HF/vLLM/SGLang serving boundaries
• update the bilingual FunClip product article and add a regression contract
• refresh the integrity manifest for the two changed legacy pages

Verification

• red phase: the new boundary test failed against exact base 2b6294d
• 100 passed in the complete product-site test suite
• 7 passed in tests/test_moss_transcribe_diarize_docs.py
• both changed legacy page SHA-256 values match legacy-manifest.json
• git diff --check passed

The first PR head exposed the missing manifest refresh in CI. That exact failure was reproduced and fixed before this update.

Exact signed+DCO head: bb66f4a.