Normalize agent instructions and workplan frontmatter (STATE-WP-0067)

- Align agent files with on-disk workplan prefixes (infer from workplan ids)
- Set workplan domain to registered domain_slug; add topic_slug where applicable
- Repair frontmatter delimiter formatting; migrate legacy task status literals
- Regenerate AGENTS.md, CLAUDE.md, and .claude/rules from State Hub templates

workplans/ARTIFACT-STORE-WP-0004-s3-compatible-backend.md

@@ -3,7 +3,7 @@ id: ARTIFACT-STORE-WP-0004
 type: workplan
 title: "S3-Compatible Backend (Ceph RGW Target)"
 repo: artifact-store
-domain: stack
+domain: infotech
 status: done
 owner: codex
 topic_slug: stack