新增 GitHub Actions 自动编译工作流

- Push/PR → main：go vet + 5 平台交叉编译验证
- Push tag v*：自动编译并发布 GitHub Release
- 编译目标：linux/amd64、linux/arm64、windows/amd64、darwin/amd64、darwin/arm64
- CGO_ENABLED=0 纯静态二进制（modernc.org/sqlite 无需 CGO）

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: holll

.github/workflows/build.yml

@@ -0,0 +1,84 @@
+name: Build & Release
+
+on:
+  push:
+    branches: [main]
+    tags: ['v*']
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    name: Build (${{ matrix.goos }}/${{ matrix.goarch }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - goos: linux
+            goarch: amd64
+          - goos: linux
+            goarch: arm64
+          - goos: windows
+            goarch: amd64
+          - goos: darwin
+            goarch: amd64
+          - goos: darwin
+            goarch: arm64
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      # 只在 linux/amd64 运行 vet，避免重复
+      - name: Vet
+        if: matrix.goos == 'linux' && matrix.goarch == 'amd64'
+        run: go vet ./...
+
+      - name: Build
+        env:
+          GOOS: ${{ matrix.goos }}
+          GOARCH: ${{ matrix.goarch }}
+          CGO_ENABLED: "0"
+        run: |
+          EXT=""
+          [ "${{ matrix.goos }}" = "windows" ] && EXT=".exe"
+          OUTPUT="tikdownloader-${{ matrix.goos }}-${{ matrix.goarch }}${EXT}"
+          go build -trimpath -ldflags="-s -w" -o "${OUTPUT}" .
+          echo "Built: ${OUTPUT}"
+
+      # 仅在 tag 触发时上传产物，供 release 作业使用
+      - name: Upload artifact
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: actions/upload-artifact@v4
+        with:
+          name: tikdownloader-${{ matrix.goos }}-${{ matrix.goarch }}
+          path: tikdownloader-${{ matrix.goos }}-${{ matrix.goarch }}*
+          if-no-files-found: error
+
+  release:
+    name: Publish Release
+    needs: build
+    if: startsWith(github.ref, 'refs/tags/v')
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Download all artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: dist
+          merge-multiple: true
+
+      - name: List artifacts
+        run: ls -lh dist/
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: dist/*
+          generate_release_notes: true
+          fail_on_unmatched_files: true