ci: 新增 GitHub Actions 编译与发布 workflow

build.yml：push/PR 到 main 及手动触发时编译，产物上传 artifact。release.yml：push v* tag 或手动触发时构建并发 GitHub Release，版本号从 tag 推导（v0.1 → 0.1），用 -Pmod_version 覆盖。均用 JDK 25（temurin），直接 ./gradlew，不依赖额外 action。

.github/workflows/build.yml

@@ -0,0 +1,34 @@
+name: Build
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 25
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '25'
+
+      - name: Grant execute permission for gradlew
+        run: chmod +x gradlew
+
+      - name: Build with Gradle
+        run: ./gradlew build --stacktrace
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: mod-jar
+          path: build/libs/*.jar
+          if-no-files-found: error