docs: rep4 bake-off write-up, MkDocs site, artifact-registry-backed experiments

docs/rep4-optimizer-results.md is the main deliverable: the model bake-off +
threshold re-tune experiment log, including the ROCm teardown deadlock root
cause and fix, DE concurrency tuning, the 16-combo results table, held-out
validation against 5 films never seen by the optimizer (macro F1 67.4% vs.
75.3% training — a real generalization gap), the frozen-bbox "ghost track"
failure mode found via annotated frame evidence, calibration curves per model,
and an isolated-effects breakdown of gallery scope vs. pose expansion.

MkDocs site (mkdocs.yml, docs/index.md) renders docs/*.md; scripts/docs/
pulls referenced images from the artifact registry and generates the
calibration chart at build time (see the tooling commit) rather than
committing images to the repo.

experiments/ now keeps only scripts + README + SESSION_STATE.md in git — every
data artifact (galleries, dumps, X-Ray corpus, montage frames, trajectories,
manifests, results) moved to the Gitea package registry. film-lut.template.json
is the committed placeholder for the gitignored file-lut.json (real local
movie paths, never shared — some source filenames carry scene-release tags).

Adds models/transnetv2.onnx (via Git LFS, matching the other ONNX models) for
the new scene-detection path.

experiments/.gitignore

@@ -0,0 +1,21 @@
+# experiments/ in git keeps only scripts, README.md, SESSION_STATE.md, and this
+# file. Every data artifact — galleries, embedding dumps, the X-Ray corpus,
+# montage/frame images, DE trajectories, film manifests, and result summaries —
+# is pushed/pulled via scripts/artifacts/{push,pull}_artifacts.sh to the Gitea
+# generic package registry instead (see docs/rep4-optimizer-results.md).
+xray/
+dumps/
+galleries/
+*.h5
+manifests/
+trajectories/
+results/
+
+# Raw run logs and scratch scripts (regenerated by every run).
+_scratch/
+
+# Real local media paths (film slug -> path on this machine). Never committed —
+# these paths embed the specific source file names, which can include
+# scene-release tags. Only file-lut.template.json (placeholders) is tracked;
+# copy it to file-lut.json and fill in your own paths.
+file-lut.json