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>

data/README.md

@@ -10,6 +10,8 @@ data/
     visible/      Per-mark example gallery: one synthetic canonical example per
                   registered mark plus documented provider originals where available
                   (see fixtures/visible/README.md)
+    synthetic/    Frozen synthetic renders that unit tests stamp onto frames, each
+                  produced by the script named in the test that loads it
   captures/
     2026-09/      Provider outputs from the maintainer's own accounts, stored as
                   served, indexed by manifest.csv (see its README)