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>

.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