fix: 修复缩略图显示权限问题，使用base64数据URL

解决asset.localhost访问权限问题:
- 添加read_thumbnail_as_data_url命令读取文件并转换为base64数据URL
- 避免使用convertFileSrc的asset.localhost协议访问问题
- 添加base64依赖支持文件编码

 优化缩略图加载:
- 使用数据URL直接在img标签中显示缩略图
- 正确处理Windows长路径前缀 \\\\?\\
- 统一错误处理和降级机制

 技术改进:
- 移除不再使用的convertFileSrc导入
- 添加详细的控制台日志便于调试
- 确保跨平台文件路径兼容性

现在缩略图可以正确显示，不会因为权限问题导致加载失败。

apps/desktop/src-tauri/Cargo.toml

@@ -18,7 +18,7 @@ crate-type = ["staticlib", "cdylib", "rlib"]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
-tauri = { version = "2", features = [] }
+tauri = { version = "2", features = ["protocol-asset"] }
 tauri-plugin-opener = "2"
 tauri-plugin-fs = "2"
 tauri-plugin-dialog = "2"
@@ -33,6 +33,7 @@ thiserror = "1.0"
 dirs = "5.0"
 md5 = "0.7"
 lazy_static = "1.4"
+base64 = "0.22"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "chrono"] }
 tracing-appender = "0.2"