Replace Coveralls badge with self-hosted coverage badge on GitHub Pages

Mirrors the active_admin_sidebar setup. SimpleCov already runs in the
coverage job; this commit adds:

- A step that reads coverage/.last_run.json, picks a shields.io color
  bucket, and writes a static badge.json in the shields endpoint format
- An upload-artifact step for the badge
- A deploy-coverage job (master pushes only) that downloads the badge
  and deploys it to GitHub Pages via actions/deploy-pages@v4
- Top-level permissions block (contents/pages/id-token) required by
  the Pages deployment actions

The README badge is switched from the dead Coveralls endpoint (no
workflow has pushed to it for years) to a shields.io endpoint badge
pointing at the new gh-pages-served badge.json.

After merging, the Pages source needs to be flipped from the legacy
gh-pages branch to "GitHub Actions" workflow build, after which the
gh-pages branch can be deleted.

Author: Fivell

.github/workflows/test.yml

@@ -3,6 +3,12 @@ on:
   pull_request:
   push:
     branches: [master]
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
 jobs:
   test:
     name: Ruby ${{ matrix.ruby }} / Rails ${{ matrix.rails }} / AA ${{ matrix.activeadmin }} / SQLite
@@ -108,3 +114,49 @@ jobs:
         with:
           name: coverage
           path: coverage/
+
+      - name: Generate badge.json
+        run: |
+          LAST_RUN="coverage/.last_run.json"
+          if [ ! -f "$LAST_RUN" ]; then
+            mkdir -p badge
+            echo '{"schemaVersion":1,"label":"coverage","message":"unknown","color":"lightgrey"}' > badge/badge.json
+            exit 0
+          fi
+          PERCENT=$(ruby -rjson -e "puts JSON.parse(File.read('$LAST_RUN')).dig('result','line').round(1)")
+          PERCENT_NUM=$(ruby -rjson -e "puts JSON.parse(File.read('$LAST_RUN')).dig('result','line')")
+          if ruby -e "exit(($PERCENT_NUM >= 90) ? 0 : 1)"; then COLOR="brightgreen"
+          elif ruby -e "exit(($PERCENT_NUM >= 75) ? 0 : 1)"; then COLOR="green"
+          elif ruby -e "exit(($PERCENT_NUM >= 60) ? 0 : 1)"; then COLOR="yellow"
+          else COLOR="red"; fi
+          mkdir -p badge
+          echo "{\"schemaVersion\":1,\"label\":\"coverage\",\"message\":\"${PERCENT}%\",\"color\":\"${COLOR}\"}" > badge/badge.json
+
+      - name: Upload badge artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-badge
+          path: badge
+
+  deploy-coverage:
+    needs: coverage
+    if: github.ref == 'refs/heads/master' && github.event_name == 'push'
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Download coverage badge
+        uses: actions/download-artifact@v4
+        with:
+          name: coverage-badge
+          path: .
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: .
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4

README.md

@@ -1,10 +1,10 @@
 # ActiveAdminImport
 
-[![Build Status   ][build_badge]][build_link]
-[![Coverage Status][coveralls_badge]][coveralls_link]
-[![Code Climate   ][codeclimate_badge]][codeclimate_link]
-[![Gem Version    ][rubygems_badge]][rubygems_link]
-[![License        ][license_badge]][license_link]
+[![Build Status][build_badge]][build_link]
+![Coverage][coverage_badge]
+[![Code Climate][codeclimate_badge]][codeclimate_link]
+[![Gem Version][rubygems_badge]][rubygems_link]
+[![License][license_badge]][license_link]
 
 
 The fastest and most efficient CSV import for Active Admin with support for validations, bulk inserts, and encoding handling.
@@ -331,8 +331,7 @@ Tool                  | Description
 
 [build_badge]: https://github.com/activeadmin-plugins/active_admin_import/actions/workflows/test.yml/badge.svg
 [build_link]: https://github.com/activeadmin-plugins/active_admin_import/actions
-[coveralls_badge]: https://coveralls.io/repos/activeadmin-plugins/active_admin_import/badge.svg
-[coveralls_link]: https://coveralls.io/github/activeadmin-plugins/active_admin_import
+[coverage_badge]: https://img.shields.io/endpoint?url=https://activeadmin-plugins.github.io/active_admin_import/badge.json
 [codeclimate_badge]: https://codeclimate.com/github/activeadmin-plugins/active_admin_import/badges/gpa.svg
 [codeclimate_link]: https://codeclimate.com/github/activeadmin-plugins/active_admin_import
 [rubygems_badge]: https://badge.fury.io/rb/active_admin_import.svg