Feature: Add ability to batch comments instead of submitting one by one

## Feature Request

Add the ability to write multiple comments and submit them all at once, similar to GitHub's "Start a review" feature.

## Problem

- Each comment triggers a separate notification
- Can't review all comments before sending
- Creates notification spam for reviewers
- No way to provide cohesive feedback across multiple files

## Proposed Solution

### Batch Comment Mode

1. **Start Review**: Click "Start review" button instead of immediate comment submission
2. **Add Comments**: Write multiple comments across different files/lines (marked as "pending")
3. **Submit All**: Submit all pending comments at once with optional summary

### Key Features

- Visual indicators for pending comments
- Edit/delete pending comments before submission
- Preview all pending comments
- Submit with review status (comment/approve/request changes)
- Auto-save drafts locally
- Single notification for all comments

### UI Elements

- Batch mode indicator with pending comment count
- "Pending" badge on unsent comments
- Submit review button with comment summary option
- Clear visual distinction between pending and submitted comments

## Benefits

- One notification instead of many
- Better organized feedback
- Ability to review before sending
- Can cancel if needed

## Acceptance Criteria

- [ ] Can enter/exit batch mode
- [ ] Add multiple comments without immediate submission
- [ ] Edit/delete pending comments
- [ ] View all pending comments
- [ ] Submit all at once
- [ ] Drafts persist through refresh
- [ ] Clear batch mode indicators
- [ ] Single notification sent

## Similar To

- GitHub's "Start a review" for PRs
- GitLab's batch comments
- Bitbucket's draft comments

🤖 Generated with [Claude Code](https://claude.ai/code)

No files, tests, or entry points are named. First map the existing comment submission and review UI, then determine how pending comments, local drafts, refresh persistence, review status, and notifications are handled; done means all listed acceptance criteria work together.

Written by the indexing model from the issue text.