feat: implement persistent sidebar state management

[fx]

Closes #74

Summary

• Added sidebar state (sidebarOpen and sidebarPinned) to the dashboard configuration
• Implemented persistence of sidebar state to localStorage
• Updated export/import functionality to include sidebar state in both JSON and YAML formats
• Added proper actions for toggling sidebar state that mark the state as dirty
• Created comprehensive tests for sidebar state persistence

Changes Made

Configuration Updates

• Added sidebarOpen and sidebarPinned to DashboardConfig interface
• Updated exportConfiguration to include sidebar state
• Updated loadConfiguration to restore sidebar state (with fallback to current state)
• Updated YAML export to include sidebar properties

Store Actions

• Modified toggleSidebar action to mark state as dirty
• Added new toggleSidebarPin action for pin state management
• Updated TabSidebar component to use proper actions instead of direct state updates

Testing

• Created comprehensive test suite for sidebar persistence
• Tests cover export, import, localStorage persistence, and dirty state management
• All tests passing

Testing

• Tested sidebar state persists across page reloads
• Verified state is included in JSON export
• Verified state is included in YAML export
• Confirmed import restores sidebar state correctly
• All unit tests pass
• TypeScript checks pass
• Linting passes

Epic: #72