白名单确认:PR #1274 feat(providers): allow setting context window for manually added custom models

PR: https://github.com/makecindy/cindy/pull/1274
作者: MisterMyth

**触发原因**: feat 类型 + 命中 UI 路径 `apps/desktop/src/renderer/components/settings/AddProviderWizard.tsx`

该 PR 为手动添加的自定义模型增加上下文窗口设置入口,涉及产品交互变更。

**放行方式**: roster 任一成员在 PR 上提交 GitHub Approve 即放行;若需修改请 Request Changes,作者改完后重新 Approve。

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关联 PR:#1274(作者 @MisterMyth);本 issue 由 review-pr 流程自动创建,用于先讨论该 PR 涉及的产品 / UI 变更,维护者确认后 PR 会恢复推进。

Review PR #1274 and the mentioned entry point, apps/desktop/src/renderer/components/settings/AddProviderWizard.tsx. Check how the custom-model context-window setting changes the product interaction, then confirm whether the UI change is acceptable; done means a roster member approves the PR or requests changes.

Written by the indexing model from the issue text.