ci(docs): notify ntfy when main build fails

Adds an `if: failure()` step that POSTs to ntfy.sh on a failed push-to-main
run. Topic comes from the NTFY_TOPIC secret so it stays out of the public
repo; missing secret silently no-ops via `|| true`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.forgejo/workflows/docs.yml

@@ -46,3 +46,16 @@ jobs:
       - name: Publish to /output (main only)
         if: github.ref == 'refs/heads/main' && github.event_name == 'push'
         run: rsync -a --delete site/ /output/
+
+      - name: Notify ntfy on failure
+        if: failure() && github.ref == 'refs/heads/main' && github.event_name == 'push'
+        run: |
+          curl -sf \
+            -H "Title: docs.makerfloss.eu build failed" \
+            -H "Priority: high" \
+            -H "Tags: warning,rotating_light" \
+            -d "Run #${{ github.run_number }} on ${{ github.ref_name }}@${{ github.sha }}
+          ${{ github.event.head_commit.message }}
+
+          ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}" \
+            "https://ntfy.sh/${{ secrets.NTFY_TOPIC }}" || true