infra: CI workflow 작성

- 코드 통합 이전에 오류 검출을 위함

Author: ysw789

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [ "dev" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/[email protected]
+
+      - name: Set up JDK 21
+        uses: actions/[email protected]
+        with:
+          distribution: 'temurin'
+          java-version: '21'
+          cache: gradle
+
+      - name: Grant execute permission for gradlew
+        run: chmod +x gradlew
+
+      - name: Build with Gradle
+        run: ./gradlew clean build