Introduce a three-state checkbox in CanvasLayersPanel header to control visibility of all layers at once. Supports automatic state updates and integrates with renderLayers() for seamless layer management.
Added updateButtonStates() to enable/disable delete button based on selection
Updated control setup and selection handlers to call this method
Added CSS for disabled button state and tooltip
Delete button now disables when no layers are selected; all other panel features unchanged
Moved all inline styles from CanvasLayersPanel.ts to layers_panel.css
Updated TypeScript to load external CSS and removed injectStyles()
Replaced inline styles with CSS classes in UI methods
Ensured all panel features and interactions work as before
Improved code maintainability and consistency with project structure
