[Requests and ideas] Hope to support adding a subfolder of a folder managed by git

**Mood**: 😊
**Category**: Requests and ideas

Hope to support adding a subfolder of a folder managed by git
Background: For monorepo, one git manages multiple sub-projects (such as iOS/Android). For an iOS developer, he only cares about iOS projects. But currently if I just want to add the iOS folder to the github copilot app, the actual effect is to add the root directory of the monorepo, which is too big.

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| Field | Value |
| --- | --- |
| App version | 0.2.33 |
| OS | macOS 26.5.1 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Day 1 |

Start by tracing how the app currently adds folders managed by Git and how it determines the repository root. Define the selection behavior for a subfolder in a monorepo, including what should happen when the user adds the iOS folder, and verify that only the selected project scope is used.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.