docs: richer report — data figures, success/failure frames, commit-pinned repo links

- experiment_charts.py generates 4 figures from experiments/ artifacts:
  held-out per-film F1, 16-combo ranking, DE search landscape, and the
  Downton detector-vs-tracker ghost timeline (replaces the blank
  title-card screenshot)
- new frames: 19-correct wedding shot (success case), Many Saints
  ghost-vs-unknown frame (three error classes in one image)
- rename rep4-optimizer-results.md -> model-bakeoff.md; rep4 kept only
  as the on-disk artifact prefix, explained once
- repo file references are now links via https://REPOLINK/<path>
  placeholders; build_site.sh pins them to the HEAD commit's raw URLs
  and fails the build if a linked path doesn't exist at HEAD
- drop references to removed scripts (scene_score.py, score_config.py)
  and to session-memory names; mark artifact-registry paths with their
  pull commands
- commit readme_example.jpg + pipeline_topology.svg so README renders
  on the plain Gitea repo view
- deploy_pages.sh: push built site/ to the gitea-pages branch

.gitignore

@@ -78,7 +78,16 @@ docs_site/
 
 # Images staged into docs/ from the artifact registry at build time
 # (scripts/docs/build_site.sh) — not committed, pulled fresh on each build.
-docs/assets/
+# Exception: pipeline_topology.svg is small and hand-authored (not pulled from
+# anywhere) and the README references it directly, so it needs to render on a
+# plain Gitea repo view too, not just the built Pages site. (A directory-level
+# ignore can't be un-ignored file-by-file below it, so this must NOT blanket-
+# ignore docs/assets/ itself — only its contents, minus the one exception.)
+docs/assets/images/*
+!docs/assets/images/pipeline_topology.svg
+# readme_example.jpg is referenced directly by README.md, which renders on the
+# plain Gitea repo view — committed for the same reason as the SVG above.
+!docs/assets/images/readme_example.jpg
 
 # Python
 __pycache__/