redesign: playful pastel theme with solid colors, new landing page

- Rewrite all components to use Tailwind utility classes (Tailwind v4 broke custom CSS classes)
- New landing page at / with hero, features bento grid, how-it-works, privacy section
- Converter tool moved to /convert route
- Fonts: Fraunces (serif headlines) + Plus Jakarta Sans (body) + JetBrains Mono (labels)
- Warm cream palette with pastel category colors (pink, blue, purple, orange, mint)
- Remove all gradients — solid colors only throughout
- Remove floating badge bounce animation
- Responsive action bar and file grid for mobile
- Register design tokens via @theme inline for Tailwind v4 compatibility

src/types/index.ts

@@ -26,12 +26,12 @@ export interface ConversionResult {
 }
 
 export const CATEGORY_COLORS: Record<FileCategory, string> = {
-  image: '#10b981',
-  document: '#0ea5e9',
-  audio: '#8b5cf6',
-  video: '#f43f5e',
-  data: '#f59e0b',
-  unknown: '#6b7280',
+  image: '#f472b6',    // soft pink
+  document: '#60a5fa',  // soft blue
+  audio: '#a78bfa',    // soft purple
+  video: '#fb923c',    // soft orange
+  data: '#34d399',     // soft mint
+  unknown: '#94a3b8',  // soft slate
 };
 
 export const CATEGORY_ICONS: Record<FileCategory, string> = {