ci: wire governance traceability env in gitea workflow and guard zero SHA (#330)

.gitea/workflows/ci.yml

@@ -28,6 +28,9 @@ jobs:
         run: python3 scripts/session_handover_check.py --strict
 
       - name: Validate governance assets
+        env:
+          GOVERNANCE_PR_TITLE: ${{ github.event.pull_request.title }}
+          GOVERNANCE_PR_BODY: ${{ github.event.pull_request.body }}
         run: |
           RANGE=""
           if [ "${{ github.event_name }}" = "pull_request" ] && [ -n "${{ github.event.pull_request.base.sha }}" ]; then