Upgrade to OpenCV 5 with frozen Hershey templates and tighten video marks

- Lock OpenCV 5 and cap NumPy below 2.4 through uv constraint-dependencies so
  PaddleX 3.7 keeps resolving; Dependabot ignores mirror the cap.
- OpenCV 5 draws Hershey putText glyphs differently, so the Dola and Kling
  video templates ship as committed OpenCV 4 renders with a recipe script, and
  the OpenArt alpha recipe now refuses any OpenCV but 4.x.
- Break Sora/Veo cross-matches in favor of Veo under valid Google AI-video
  provenance, and require the full Sora mascot shape for mascot-only matches.
- Let the Doubao engine detect marks tinted by saturated backgrounds.
- Share C2PA claim-generator, credential-level and vendor-platform helpers,
  JPEG suffixes and the DCT basis instead of per-module copies.
- Log model download failures, document the optional GITHUB_TOKEN, mark the
  photo and source classifier model cards archived, and refresh the lock.

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
   calibration/
     <vendor>/     Minimal controlled inputs needed to rebuild detector assets
   synthid/