feat: add PR validation workflow and contribution checks

bmad-core/workflows/brownfield-fullstack.yaml

@@ -160,7 +160,7 @@ workflow:
         - Dev Agent (New Chat): Address remaining items
         - Return to QA for final approval
 
-    - repeat_development_cycle:
+    - step: repeat_development_cycle
       action: continue_for_all_stories
       notes: |
         Repeat story cycle (SM → Dev → QA) for all epic stories
@@ -177,7 +177,7 @@ workflow:
         - Validate epic was completed correctly
         - Document learnings and improvements
 
-    - workflow_end:
+    - step: workflow_end
       action: project_complete
       notes: |
         All stories implemented and reviewed!