fix: prevent UI from going blank when terminal panel is opened on macOS

[roomote]

This PR attempts to address Issue #9227. Feedback and guidance are welcome.

Problem

The Roo UI was going blank when the terminal panel was opened on macOS. This was caused by the ChatView component using fixed positioning that didn't properly adapt to viewport changes when the terminal panel resized the webview container.

Solution

• Changed ChatView from fixed positioning to absolute positioning within a relative container
• Added proper height and positioning styles to body and #root elements to ensure proper containment
• This ensures the webview content stays within container boundaries when the terminal panel resizes the viewport

Testing

• All existing tests pass (976 tests passed)
• The changes are minimal and focused on CSS positioning to avoid breaking other functionality

Fixes #9227

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Important

Fixes UI blanking issue on macOS by changing ChatView positioning to absolute and updating styles in index.css.

• Behavior:
  • Fixes UI blanking issue on macOS when terminal panel is opened by changing ChatView positioning from fixed to absolute in ChatView.tsx.
  • Ensures webview content remains within container boundaries by adding height and positioning styles to body and #root in index.css.
• Testing:
  • All existing tests pass (976 tests passed).
  • Changes are minimal and focused on CSS positioning to avoid breaking other functionality.

^{This description was created by for a2e2e51. You can customize this summary. It will automatically update as commits are pushed.}

[roomote]

Rooviewer   See task on Roo Cloud

Review complete. No issues found.

The changes appropriately address the reported UI blank issue on macOS by switching from fixed to absolute positioning with proper containment. The implementation is minimal, focused, and follows standard patterns for full-height webview layouts.

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