feat(ci): add Codecov coverage reporting and badge

Add json/json-summary reporters to vitest config, upload coverage
to Codecov after test step in CI, and add coverage badge to README.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -25,6 +25,11 @@ jobs:
       - run: npm run lint
       - run: npm run typecheck
       - run: npm test
+      - uses: codecov/codecov-action@v5
+        if: always()
+        with:
+          files: coverage/coverage.json
+          fail_ci_if_error: false
       - run: mkdir -p dist
       - run: npm run test:cf
 

README.md

@@ -3,6 +3,7 @@
 **The open-source, S3-native file hosting platform.**
 
 [![CI](https://github.com/saltbo/zpan/actions/workflows/ci.yml/badge.svg)](https://github.com/saltbo/zpan/actions/workflows/ci.yml)
+[![codecov](https://codecov.io/gh/saltbo/zpan/graph/badge.svg)](https://codecov.io/gh/saltbo/zpan)
 [![Release](https://github.com/saltbo/zpan/actions/workflows/release.yml/badge.svg)](https://github.com/saltbo/zpan/actions/workflows/release.yml)
 [![GitHub Release](https://img.shields.io/github/v/release/saltbo/zpan)](https://github.com/saltbo/zpan/releases/latest)
 [![Docker Image](https://img.shields.io/badge/ghcr.io-saltbo%2Fzpan-blue)](https://ghcr.io/saltbo/zpan)

vitest.config.ts

@@ -19,6 +19,11 @@ export default defineConfig({
         'src/**/*.test.ts',
         'src/i18n/index.ts',
       ],
+      reporter: ['text', 'json-summary', 'json'],
+      reporterOptions: {
+        'json-summary': { file: 'coverage-summary.json' },
+        json: { file: 'coverage.json' },
+      },
       thresholds: {
         statements: 90,
         branches: 80,