[General] No ability to add line/diff comments in the PR view.

**Mood:** 😔
**Category:** General

No ability to add line/diff comments in base PR view (not the one where we open a new copilot session with a PR). Please add that feature.

---
| Field | Value |
| --- | --- |
| App version | 0.2.32 |
| OS | macOS 26.4.1 |
| Theme | Notionish |
| Path | /mywork |
| Tenure | Day 1 |

该 issue 未提供文件、测试或入口点。首先跟踪基础 PR 视图及其现有的评论交互，并将其与 Copilot 会话 PR 视图区分开来。当用户可以在基础 PR 视图中添加行评论或 diff 评论，并且该流程在桌面应用中正常工作时，即视为完成。

由索引模型根据 Issue 内容生成。