ci: 테스트 추가

테스트를 실행하고 커버리지 결과를 codecov에 업로드합니다.

참고: https://about.codecov.io

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: CI
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+defaults:
+  run:
+    working-directory: backend
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [20, 22]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: pnpm 설치
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
+          package_json_file: "backend/package.json"
+
+      - name: Node.js ${{ matrix.node-version }} 설치
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: "pnpm"
+          cache-dependency-path: backend/pnpm-lock.yaml
+
+      - name: 의존성 설치
+        run: pnpm install
+
+      - name: 테스트
+        run: |
+          pnpm lint:ci
+          pnpm typecheck
+          pnpm test:cov
+
+      - name: Codecov에 커버리지 결과 배포
+        uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}