PR review: batch inline comments into a submittable review so the agent acts once, not per-comment

PR review: batch inline comments into a submittable review so the agent acts once, not per-comment

### Describe the feature or problem you'd like to solve

When reviewing a pull request in the desktop app's diff viewer, each inline review comment I post is dispatched to the agent **immediately and individually** — every comment triggers its own agent turn that acts right away.

This means if I'm still working through a review — leaving five comments across several files — the agent starts editing after comment #1, while I'm still writing comments #2–#5. My changes and its changes interleave, the PR "moves around" under me, and I can't compose a complete review before the agent responds.

On **GitHub web**, review comments work differently: they're collected into a **pending review** and only released together when I click **Submit review**. The reviewer finishes the entire pass first; consumers act once, on submit.

### Proposed solution

Add a **pending-review / batch-submit mode** to the diff-review experience, matching GitHub web:

- Inline comments I add accumulate as a **pending (draft) review** and are **not** sent to the agent as I type them.
- A **Submit review** action releases the whole batch at once.
- The agent then acts on the complete set in one pass, rather than reacting comment-by-comment.

Ideally this is the default (or a toggle), so the per-comment behavior becomes opt-in for people who want immediate action.

### Example prompts or workflows

- I review a 6-file PR and leave 8 comments. Today the agent starts fixing after the first comment; my later comments land while it's mid-edit. With batch submit, I finish all 8, click Submit, and the agent addresses them together — no interleaving.

### Additional context

Current workaround is to tell the agent "wait until I'm done reviewing before acting," but that's a per-session nudge, not an enforced gate — the agent can still act on a comment before I finish. A real pending-review/submit boundary solves it at the product layer. The per-comment dispatch appears specific to the desktop diff viewer; the GitHub web batched-submit model is the desired parity.

---
| Field | Value |
| --- | --- |
| App version | 1.0.21 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 4 |

Start from the desktop app's diff viewer and the current inline-comment dispatch behavior described here. Trace how comments are sent to the agent, then define the pending-review state and Submit review boundary. Done means multiple comments remain inactive until one submission and are handled together.

Written by the indexing model from the issue text.