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/dark.ts

@@ -1,7 +1,7 @@
 export const darkTheme = {
   name: 'dark' as const,
   label: 'Dark',
-  layout: 'minimal-floating',
+  layout: 'sidebar-floating' as const,
   cssVars: {
     '--background': '0 0% 3.9%',
     '--foreground': '0 0% 98%',
@@ -24,13 +24,4 @@ export const darkTheme = {
     '--ring': '187.2 85.7% 53.3%',
     '--radius': '0.75rem',
   },
-  sidebar: {
-    width: '64px',
-    collapsible: false,
-    iconsOnly: true,
-  },
-  effects: {
-    blur: '10px',
-    glow: '0 0 20px rgba(34,211,238,0.3)',
-  },
 };