Comment staging URL on the open PR after deployment

Looks up the open PR for the pushed branch via the Gitea API using the
workflow token and posts the staging URL once (skips if the same
comment already exists).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/staging.yml

@@ -44,6 +44,29 @@ jobs:
       - name: Summary
         run: echo "Deployed to https://${HOST}" >> "$GITHUB_STEP_SUMMARY"
 
+      - name: Comment staging URL on PR
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          auth="Authorization: token ${GITHUB_TOKEN}"
+          api="${GITHUB_API_URL}/repos/${GITHUB_REPOSITORY}"
+          pr=$(curl -fsS -H "$auth" "${api}/pulls?state=open&limit=50" \
+            | jq -r --arg branch "$BRANCH" '.[] | select(.head.ref == $branch) | .number' | head -n1)
+          if [ -z "$pr" ]; then
+            echo "No open PR for branch '${BRANCH}', skipping comment"
+            exit 0
+          fi
+          body="Staging deployment: https://${HOST}"
+          if curl -fsS -H "$auth" "${api}/issues/${pr}/comments" \
+            | jq -e --arg body "$body" 'any(.[]; .body == $body)' >/dev/null; then
+            echo "Staging URL already commented on PR #${pr}"
+            exit 0
+          fi
+          curl -fsS -X POST -H "$auth" -H 'Content-Type: application/json' \
+            -d "$(jq -n --arg body "$body" '{body: $body}')" \
+            "${api}/issues/${pr}/comments" >/dev/null
+          echo "Commented staging URL on PR #${pr}"
+
   teardown:
     if: github.event_name == 'delete' && github.event.ref_type == 'branch'
     runs-on: ubuntu-latest