feat(fs): add native save-from-share for cloud drivers

[hi-pengbo]

Summary / 摘要

Add a driver-level save-from-share capability so cloud storages can save files from share links into a chosen directory. Quark/UC Session implements it first; the frontend “More” menu shows the action only when the current storage supports it.

新增驱动级「分享链接转存」能力，将分享中的文件保存到指定目录。先由夸克/UC Session 实现；前端仅在当前存储支持时，在「更多」菜单中显示转存入口。

• Users can paste one or more share links (optional passcode in the same line), pick a destination folder, and save natively on the cloud drive without downloading through OpenList.
  / 用户可粘贴一条或多条分享链接（同一行可带提取码），选择目标目录后由网盘原生转存，文件不经过 OpenList 中转。

• /api/fs/list now returns save_from_share so the UI can show or hide the button.
  / /api/fs/list 新增 save_from_share，前端据此显示或隐藏按钮。

• New API: POST /api/fs/save_from_share with { path, urls, password }. Permission matches mkdir/upload (write on the destination path).
  / 新增接口 POST /api/fs/save_from_share，参数为 { path, urls, password }。权限与新建目录/上传一致（目标路径可写）。

• New optional driver interface driver.SaveFromShare. Other drivers can implement the same method without HTTP or UI changes.
  / 新增可选驱动接口 driver.SaveFromShare。其他网盘实现同一方法即可，无需改 HTTP 或前端。

• Quark/UC flow: parse link → share token → list share root → save → poll /task until completion, then invalidate directory cache.
  / 夸克/UC 流程：解析链接 → 取分享 token → 列分享根目录 → 转存 → 轮询 /task 直到完成，然后失效目录缓存。

• No config, storage-format, or migration changes.
  / 不涉及配置、存储格式或迁移变更。

• This PR has breaking changes.
  / 此 PR 包含破坏性变更。

• This PR changes public API, config, storage format, or migration behavior.
  / 此 PR 修改了公开 API、配置、存储格式或迁移行为。

• This PR requires corresponding changes in related repositories.
  / 此 PR 需要关联仓库同步修改。

Related repository PRs / 关联仓库 PR:

• OpenList:
• OpenList-Docs:

Testing / 测试

• go test ./...
• Manual test / 手动测试:
  • go test ./drivers/quark_uc/ ./internal/fs/ ./internal/op/ ./server/handles/
  • Built a local binary with the matching frontend, started ./openlist server, added a Quark Session storage, and confirmed save-from-share from the More menu into a chosen folder.
    / 使用配套前端构建本地二进制并启动 ./openlist server，添加夸克 Session 存储后，从「更多」菜单转存分享链接到指定目录，行为正常。

Did not run full go test ./....
/ 未执行完整的 go test ./...。

Checklist / 检查清单

• I have read CONTRIBUTING.
  / 我已阅读 CONTRIBUTING。
• I confirm this contribution follows the repository license, contribution policy, and code of conduct.
  / 我确认此贡献符合仓库许可证、贡献规范和行为准则。
• I have formatted the changed code with gofmt, go fmt, or prettier where applicable.
  / 我已按适用情况使用 gofmt、go fmt 或 prettier 格式化变更代码。
• I have requested review from relevant maintainers or code owners where applicable.
  / 我已在适用情况下请求相关维护者或代码所有者审查。

AI Disclosure / AI 使用声明

• This PR includes AI-assisted content.
  / 此 PR 包含 AI 辅助内容。

Tools used / 使用工具:

• ChatGPT
• Codex
• GitHub Copilot
• Claude
• Gemini
• Other (please specify) / 其他（请注明）: Grok (xAI)

Usage scope / 使用范围:

• Code generation / 代码生成

• Refactoring / 重构

• Documentation / 文档

• Tests / 测试

• Translation / 翻译

• Review assistance / 审查辅助

• I have reviewed and validated all AI-assisted content included in this PR.
  / 我已审核并验证此 PR 中的所有 AI 辅助内容。

• I have ensured that all AI-assisted commits include Co-Authored-By attribution.
  / 我已确保所有 AI 辅助提交都包含 Co-Authored-By 归属信息。

• I can reproduce all AI-assisted content included in this PR without any AI tools.
  / 我可以在没有任何 AI 工具的情况下重现此 PR 中包含的所有 AI 辅助内容。

[xrgzs]

Same #1962