[BUG] Review panel freezes when expanding large file diffs in app

[cooooooooooode]

Description

In the web/desktop app review panel, files with large diffs (500+ changed lines) are auto-expanded when opening the panel. This causes the UI to freeze or become very laggy because thousands of diff lines are rendered at once.

The current logic in packages/ui/src/components/session-review.tsx only checks file count (>10 files → collapse all), but ignores individual file diff size. A single file with 2000+ changed lines can freeze the entire review panel.

Plugins

No response

OpenCode version

No response

Steps to reproduce

1. Start a session that modifies a large file (500+ line changes)
2. Open the review panel (right side panel)
3. Observe the UI freezes while rendering the large diff

Screenshot and/or share link

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Operating System

macOS / any

Terminal

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[neriousy]

Fixed in #13460