refactor(vscode): extract shared diff review UI

[marius-kilocode]

The reusable diff review UI still lived under Agent Manager even though the standalone Changes tab and virtual diff viewer depend on the same rendering, file-tree, Markdown, and inline-review behavior. That ownership boundary made shared behavior look Agent Manager-specific and made cross-surface fixes harder to reason about.

Move the shared diff review cluster into webview-ui/diff-viewer/ and update Agent Manager, sidebar Changes, virtual diffs, Storybook, and architecture tests to import through that boundary. Agent Manager-specific orchestration and its sidebar panel remain in webview-ui/agent-manager/. Existing stylesheet imports stay attached to the shared fullscreen component so every bundle continues receiving the required styles.

Closes #10848

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (14 files)

• packages/kilo-vscode/tests/unit/agent-manager-arch.test.ts
• packages/kilo-vscode/tests/unit/agent-manager-diff-state.test.ts
• packages/kilo-vscode/tests/unit/diff-viewer-css-arch.test.ts
• packages/kilo-vscode/tests/unit/file-tree.test.ts
• packages/kilo-vscode/tests/unit/markdown-annotation-layer.test.ts
• packages/kilo-vscode/tests/unit/review-comments.test.ts
• packages/kilo-vscode/webview-ui/agent-manager/AgentManagerApp.tsx
• packages/kilo-vscode/webview-ui/agent-manager/ApplyDialog.tsx
• packages/kilo-vscode/webview-ui/agent-manager/DiffPanel.tsx
• packages/kilo-vscode/webview-ui/diff-viewer/DiffViewerApp.tsx
• packages/kilo-vscode/webview-ui/diff-viewer/FullScreenDiffView.tsx (renamed)
• packages/kilo-vscode/webview-ui/diff-virtual/DiffVirtualApp.tsx
• packages/kilo-vscode/webview-ui/src/stories/agent-manager.stories.tsx
• 10 renamed files (pure moves, no content changes)

This is a clean mechanical refactor. All import paths in tests, Agent Manager, diff-viewer, diff-virtual, and Storybook have been updated to point at the new webview-ui/diff-viewer/ location. No stale imports remain in the old agent-manager/ path. The architecture test for CSS imports (diff-viewer-css-arch.test.ts) correctly reflects the updated relative path ../agent-manager/agent-manager.css from the new location. The CSS invariant is preserved.

Fix these issues in Kilo Cloud

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_{Reviewed by claude-4.6-sonnet-20260217 · 503,376 tokens}

_{Review guidance: REVIEW.md from base branch main}