chore: ignore the benchmark corpus and derived data

hero/ and dvu-hero/ are ~140 MB of film clips, DVU annotations and the
gallery built from them. All reproducible via scripts/fetch_dvu.sh plus the
DVU movie.shots set, and the replay fixtures derived from them ship through
the artifact registry — so none of it belongs in git.

.gitignore

@@ -18,3 +18,15 @@ traces-report.json
 *.swp
 *~
 .DS_Store
+
+# Benchmark corpus and derived data — distributed as artifacts, never in git.
+# hero/ is ~130 MB of film clips and dvu-hero/ the DVU annotations and gallery
+# built from them. Both are reproducible: scripts/fetch_dvu.sh pulls the
+# annotations and mugshots, and the clips come from the DVU movie.shots set.
+# Replay fixtures derived from them ship via
+# scene-actor-extraction/scripts/artifacts/push_artifacts.sh replay-fixtures
+hero/
+dvu-hero/
+
+# Local agent session state
+.claude/