Add ntfy success/failure notifications to Docker build workflow

.github/workflows/docker-build.yml

@@ -53,3 +53,23 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+
+      - name: Notify success
+        if: success()
+        run: |
+          curl -s -X POST "${{ secrets.NTFY_URL }}" \
+            -H "Authorization: Bearer ${{ secrets.NTFY_TOKEN }}" \
+            -H "Title: check-printing built ✓" \
+            -H "Priority: default" \
+            -H "Tags: white_check_mark" \
+            -d "Image pushed: ${{ env.IMAGE_NAME }}@${{ github.sha }}"
+
+      - name: Notify failure
+        if: failure()
+        run: |
+          curl -s -X POST "${{ secrets.NTFY_URL }}" \
+            -H "Authorization: Bearer ${{ secrets.NTFY_TOKEN }}" \
+            -H "Title: check-printing build failed ✗" \
+            -H "Priority: high" \
+            -H "Tags: x" \
+            -d "Build failed on ${{ github.ref_name }} — ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"