fix(thunder): handle missing token errors

[jyxjjj]

Summary / 摘要

• 修复 Thunder 相关驱动在 token 缺失或刷新失败后触发空指针 panic 的问题。
• 将空 token 请求转为 errs.EmptyToken 普通错误，让存储加载按现有失败状态处理并继续加载其他驱动。
• 避免刷新或重新登录失败后写入 nil token，并补充 Thunder、ThunderX、Thunder Browser 的回归测试。

⚠️ 本组织、仓库、相关维护者，不对破解驱动作出任何修复、维护，本次修复，旨在允许驱动失败时，进程免于崩溃。并未修复驱动本身的问题。

• 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-Frontend:
• OpenList-Docs:

Related Issues / 关联 Issue

Fixes #2467
Fixes #2571
Fixes #2567

Testing / 测试

• go test ./...
• Manual test / 手动测试:

Checklist / 检查清单

• I have read CONTRIBUTING.
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• I confirm this contribution follows the repository license, contribution policy, and code of conduct.
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• 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。

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  / 我可以在没有任何 AI 工具的情况下重现此 PR 中包含的 AI 辅助内容。

[Copilot]

Pull request overview

This PR hardens the Thunder-family storage drivers (Thunder, ThunderX, Thunder Browser) against nil-token scenarios so token loss/refresh failures no longer trigger nil-pointer panics during request authorization, allowing storage initialization to fail gracefully without taking down the process.

Changes:

• Add early errs.EmptyToken returns in Request when the in-memory token is missing (TokenResp == nil).
• Prevent writing/using nil tokens after refresh/login attempts by returning early when token == nil.
• Add regression tests ensuring Request returns errs.EmptyToken when invoked without a token.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
drivers/thunderx/driver.go	Adds nil-guards around token usage and returns errs.EmptyToken when token is missing in Request.
drivers/thunderx/driver_test.go	Regression test for missing-token Request behavior.
drivers/thunder/driver.go	Adds nil-guards in refresh flow and returns errs.EmptyToken when token is missing in Request.
drivers/thunder/driver_test.go	Regression test for missing-token Request behavior.
drivers/thunder_browser/driver.go	Adds errs import and missing-token handling in Request, plus refresh-flow nil-guard.
drivers/thunder_browser/driver_test.go	Regression test for missing-token Request behavior.

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