feat: add optional cc-switch compatibility mode

[WhiskyChoy]

Summary / 概述

Users who rely on cc-switch or similar environment-switching workflows cannot fully preserve their initial Claude defaults inside CodePilot today.

目前依赖 cc-switch 或类似环境切换工作流的用户，无法在 CodePilot 中完整保留最初的 Claude 默认状态。

Current pain points / 当前痛点

• the built-in env provider can be auto-healed away even when the user intentionally wants it as the default provider

• the selected effort level is not locked in as a stable provider default for the next new chat

• 即使用户明确希望把内置 env 作为默认提供商，它也可能被自动修复逻辑替换掉

• 已选择的 effort 不能稳定地作为该提供商的默认值带到下一个新对话

Expected behavior / 期望行为

Add an optional compatibility toggle in Settings so users can explicitly opt into cc-switch-style behavior.

在设置中增加一个可选兼容开关，让用户可以显式启用与 cc-switch 一致的行为。

When enabled:

• keep env as a valid default provider target
• persist and restore the provider-level effort selection for new chats
• expose the option with proper i18n text so both English and Chinese users can understand it

开启后应当：

• 保留 env 作为有效的默认提供商目标
• 持久化并恢复提供商级别的 effort 选择，让新对话延续默认值
• 提供完整的多语言文案，确保中英文用户都能理解该选项

References / 参考

• WhiskyChoy/CodePilotPersist
• farion1231/cc-switch

[StoneLL1]

支持