Add self-scoping assessment export command

docs/self-scoping/README.md

@@ -33,3 +33,18 @@ assessment. Compare the challenger to the golden profile and to the negative
 seed. Reviewers should be able to choose whether the old result, new result, or
 neither is better, then store that judgement as a new assessment outcome.
 
+## Export Command
+
+Export a completed analysis run as a challenger artifact:
+
+```bash
+repo-scoping export-assessment \
+  --repo repo-scoping \
+  --analysis-run 39 \
+  --output docs/self-scoping/assessments/repo-scoping-challenger-run-39.json
+```
+
+The command reads an existing registry database and does not clone or scan the
+target repository. It records the target analysis metadata, candidate graph,
+approved map at export time, review decisions, fact and content summaries, known
+regression patterns, and current repo-scoping engine identity.