feat: enable automatic auth credential updates by default and improve auth handling

[bbbugg]

中文

• 默认开启: 将 ENABLE_AUTH_UPDATE 环境变量默认值设为 true。
• 切换自动保存: 增加逻辑：在切换账号前，自动保存旧账号的最新 Auth 状态。

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English

• Default Enabled: Changed ENABLE_AUTH_UPDATE default to true.
• Auto-Save on Switch: Added logic to automatically save the old account's Auth state before switching.

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front pr #21

[Copilot]

Pull request overview

This pull request enables automatic authentication credential updates by default and adds logic to save the current account's authentication state before switching to a different account. The changes improve auth handling by making credential persistence more robust and reducing the risk of losing session data during account switches.

Changes:

• Changed default value of ENABLE_AUTH_UPDATE from false to true and modified environment variable parsing to use opt-out logic
• Added automatic auth state saving before account switches in BrowserManager
• Updated JSDoc return type annotation for translateOpenAIToGoogle to reflect its async nature

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/utils/ConfigLoader.js	Changed default for enableAuthUpdate to true and modified environment variable parsing to treat anything other than "false" as enabled
src/core/BrowserManager.js	Added logic to save current auth state before switching accounts; improved condition check for periodic auth updates
src/core/FormatConverter.js	Updated JSDoc to indicate method returns a Promise
README.md	Updated documentation to reflect new default behavior for ENABLE_AUTH_UPDATE
README_EN.md	Updated documentation to reflect new default behavior for ENABLE_AUTH_UPDATE

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[github-actions]

🎉 此 PR 的修改已在版本 v0.4.0 中发布。
🎉 The changes in this PR have been released in version v0.4.0.