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/light.ts

@@ -1,7 +1,7 @@
 export const lightTheme = {
   name: 'light' as const,
   label: 'Light',
-  layout: 'sidebar-fixed',
+  layout: 'sidebar-standard' as const,
   cssVars: {
     '--background': '0 0% 100%',
     '--foreground': '222.2 84% 4.9%',
@@ -24,8 +24,4 @@ export const lightTheme = {
     '--ring': '221.2 83.2% 53.3%',
     '--radius': '0.5rem',
   },
-  sidebar: {
-    width: '240px',
-    collapsible: false,
-  },
 };