perf(app): collapse large diffs in review panel to prevent UI freeze

[cooooooooooode]

Fixes #13297

What

Review panel freezes when files with large diffs (500+ lines) are auto-expanded.

Why

The existing logic only checks total file count to decide expand/collapse, ignoring individual diff size. A single 2000-line diff can lock up the UI.

How

• Files with additions + deletions > 500 are collapsed by default
• "Expand All" skips large files
• Click-to-confirm: first click shows line count warning, second click within 3s expands
• Auto-collapse large files when review panel unmounts (persisted state cleanup)
• Added i18n keys (largeDiff.label, largeDiff.clickToExpand) across all 16 locales

Verification

1. Open a session with a large file change (500+ lines)
2. Open review panel → large file should be collapsed, showing line count
3. Click the file header → warning appears ("1234 lines — click again to expand")
4. Click again within 3s → file expands
5. Wait 3s without clicking → warning disappears, resets to initial state
6. Click "Expand All" → only small files expand
7. Close review panel, reopen → large files are collapsed again

[github-actions]

Hey! Your PR title perf(ui): collapse large diffs in review panel to prevent UI freeze doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.