feat(theme): 尝试适配 1.0.5 更新，实现背景自定义功能

- 新增主题配置项，允许用户通过 Komari 后台自定义背景图片、切换时间和过渡效果。
- 更新 GitHub Actions 发布流程，改用 `softprops/action-gh-release@v2` 以简化发布和资产上传步骤。
- 为国旗图片添加懒加载（`loading="lazy"`），优化页面加载性能。

.github/workflows/build.yaml

@@ -81,24 +81,13 @@ jobs:
 
       - name: Create Release
         if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
-        id: create_release
-        uses: actions/create-release@v1
+        uses: softprops/action-gh-release@v2
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
-          tag_name: ${{ github.ref }}
-          release_name: Release ${{ github.ref_name }}
+          tag_name: ${{ github.ref_name }}
+          name: Release ${{ github.ref_name }}
           body: ${{ env.CHANGELOG }}
           draft: false
           prerelease: false
-
-      - name: Upload Release Asset
-        if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
-        uses: actions/upload-release-asset@v1
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        with:
-          upload_url: ${{ steps.create_release.outputs.upload_url }}
-          asset_path: ./${{ env.ZIP_NAME }}
-          asset_name: ${{ env.ZIP_NAME }}
-          asset_content_type: application/zip
+          files: ${{ env.ZIP_NAME }}