feat: add theme-based layouts

Each theme now has a unique layout:
- Light: Standard fixed sidebar
- Vibrant: Horizontal top navigation
- Corporate: Compact sidebar (expands on hover)
- Dark: Floating sidebar with glass effect

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/themes/index.ts

@@ -12,5 +12,6 @@ export const themes = {
 
 export type ThemeName = keyof typeof themes;
 export type Theme = (typeof themes)[ThemeName];
+export type LayoutType = 'sidebar-standard' | 'topnav' | 'sidebar-compact' | 'sidebar-floating';
 
 export { lightTheme, vibrantTheme, corporateTheme, darkTheme };