feat: mcp UI sidecar (WIP)

[Kvadratni]

Add MCP UI sidecar panel for interactive tool interfaces

This PR introduces a collapsible sidecar panel that displays MCP UI resources alongside the main chat interface. When tools return UI resources (like forms, visualizations, or interactive components), users can open them in a dedicated side panel for better interaction.

Key Features:

• Toggle button appears on tool responses with UI resources
• Sidecar panel slides in from the right with smooth animations
• Window automatically resizes to accommodate the panel
• Context shared between main chat and sidecar for seamless interaction
• Clean separation of concerns with dedicated SidecarContext

Technical Implementation:

• New SidecarContext manages panel state and UI resource handling
• MainPanelLayout updated to support flexible width with sidecar
• IPC communication for window resizing when panel opens/closes
• Responsive design maintains usability across different screen sizes

mcp-ui-sidecar-compressed.mp4