feat(visual-editor): Add frontend assets for editor UI and block styles

Add CSS and JavaScript for the visual editor:

CSS (resources/css/):
- editor.css: Complete editor UI styles including toolbar, panels,
  canvas, layers tree, context menu, drag-drop indicators
- blocks.css: Frontend block rendering styles with responsive design

JavaScript (resources/js/):
- visual-editor.js: Alpine.js components for canvas, block panel,
  layers tree, settings panel, and AI assistant
- Drag-and-drop support with HTML5 API
- Keyboard shortcuts (copy, paste, delete, undo, redo)
- Context menu for block actions

Features:
- Dark mode support via CSS variables
- Responsive viewport preview (desktop, tablet, mobile)
- Drop indicators and visual feedback during drag operations
- Collapsible panel sections and categories

Author: claude