feat(ci): add coverage badge generation

Add automatic coverage badge SVG generation using
jaywcjlove/coverage-badges-cli action.

Changes:
- Add json-summary reporter to vitest coverage config
- Generate badges.svg from coverage-summary.json in CI
- Badge will be available at GitHub Pages URL/badges.svg

This enables adding a coverage badge to README that automatically
updates when coverage changes.

Author: ryoppippi

.github/workflows/ci.yaml

@@ -45,6 +45,13 @@ jobs:
         if: github.ref == 'refs/heads/main'
         run: nix develop --command pnpm run coverage
 
+      - name: Create Coverage Badge
+        if: github.ref == 'refs/heads/main'
+        uses: jaywcjlove/coverage-badges-cli@e07f25709cd25486855c1ba1b26da53476dfb763 # v2.3.2
+        with:
+          source: coverage/coverage-summary.json
+          output: coverage/badges.svg
+
       - name: Upload coverage artifact
         if: github.ref == 'refs/heads/main'
         uses: actions/upload-pages-artifact@7b1f4a764d45c48632c6b24a0339c27f5614fb0b # v4.0.0

vitest.config.ts

@@ -7,7 +7,7 @@ export default defineConfig({
     testTimeout: 30000,
     coverage: {
       provider: 'v8',
-      reporter: ['text', 'json', 'html'],
+      reporter: ['text', 'json', 'json-summary', 'html'],
       include: ['src/**/*.ts', 'examples/**/*.ts'],
       exclude: ['**/*.spec.ts', '**/*.test.ts', '**/*.test-d.ts', '**/tests/**'],
     },