Merge origin/main into docs/library-research-landscape

Main's claim_generator_platform and c2pa_vendor_platform now use the
branch's whole-word registry match, which replaces
claim_generator_word_platform. The branch's provenance veto covers every
video mark and made main's Veo-over-Sora override unreachable, so the
override is removed. Main's credential rule carries into the veto: an
invalid credential vetoes nothing. Provenance that confirms the mark's
own vendor also vetoes nothing. Over 78 local videos with a C2PA AI
claim, the only verdict changes against main are Kling/Hailuo false
positives on Veo and FLUX clips that the veto now removes. C2PA verdicts
over 1,379 files are unchanged against the pre-merge branch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.env.example

@@ -6,6 +6,10 @@
 # Create and manage keys at: https://platform.openai.com/api-keys
 # OPENAI_API_KEY=
 
+# GitHub token (optional; only for scripts/sync_c2pa_soft_bindings.py)
+# Raises the api.github.com rate limit from 60 to 5000 requests/hour. GH_TOKEN is read as a fallback.
+# GITHUB_TOKEN=
+
 # Local photo-classifier weights (optional; otherwise fetched from Hugging Face)
 # Directory contents are documented in docs/photo-classify.md.
 # RAIW_CLASSIFY_WEIGHTS=/path/to/classifier-weights