Improve diff viewer window resizing and sidecar transitions

[aharvard]

Overview

This PR addresses window resizing issues in the diff viewer sidecar functionality and lays groundwork for improved transitions.

Changes Made

• Fixed window resizing toggle behavior: The useWindowManager hook now properly handles both expansion and collapse states when toggling the diff viewer
• Improved wide window handling: Windows that are already wide enough (>2200px) now properly show the sidecar without unnecessary resizing
• Enhanced state management: Fixed edge cases where the window state could become inconsistent during toggle operations

Issues Addressed

• ✅ Window growing too wide when clicking "View Diff" button repeatedly
• ✅ Sidecar not closing properly when clicking "View Diff" again
• ✅ Window not returning to original size when sidecar is closed
• ✅ Proper handling of windows that are already wide enough

Future Improvements Planned

• Smoother transitions: Planning to refine the timing so the chat area doesn't become awkwardly wide before the sidecar appears
• Slide-in animation: Working on making the sidecar slide in smoothly from the right side for a more polished user experience

Testing

• Tested window expansion/collapse toggle functionality
• Verified behavior on both narrow and wide windows
• Confirmed sidecar shows/hides correctly
• Tested edge cases with rapid clicking

Technical Details

The main changes are in:

• src/hooks/useWindowManager.ts: Fixed toggle logic to handle both expand and collapse states
• src/components/SidecarLayout.tsx: Updated to properly call window collapse when hiding views
• src/components/GooseMessage.tsx: Enhanced to check sidecar state and toggle appropriately
• src/components/CheckpointActions.tsx: Added sidecar integration for consistent behavior

This provides a solid foundation for the upcoming transition improvements and slide-in animations.

[aharvard]

two things are still bothering me

1. the chat message thread grows when the window resizes. I think its width should remain as-is.
2. the sidecar does not slide in from the right

not blockers, but I'm gonna try to address those before my EOD