feat: implement Phase 3 - Advanced UX features and interactivity

Add comprehensive UX enhancements with innovative features:

🔍 Fuzzy Search Component (SearchUnits.tsx):
- Powered by Fuse.js for intelligent fuzzy matching
- Searches across unit abbreviations, names, and categories
- Real-time dropdown with results
- Keyboard shortcut: Press "/" to focus search
- Press Escape to close
- Click outside to dismiss
- Shows measure category with color dot
- Top 10 results displayed
- Smart weighting: abbr (2x), singular/plural (1.5x), measure (1x)

💾 Conversion History (ConversionHistory.tsx):
- LocalStorage persistence (max 50 entries)
- Auto-saves conversions as user types
- Collapsible history panel
- Click to restore previous conversion
- Clear all with confirmation
- Shows relative time (just now, 5m ago, etc.)
- Live updates across tabs with storage events
- Custom event dispatch for same-window updates

🌓 Dark Mode Support:
- ThemeProvider with light/dark/system modes
- Persistent theme preference in localStorage
- Smooth theme transitions
- ThemeToggle component with animated sun/moon icons
- Gradient text adapts to theme
- System preference detection

⭐ Favorites & Copy Features:
- Star button to favorite units (localStorage)
- Copy to clipboard with visual feedback
- Hover to reveal action buttons
- Check icon confirmation for 2 seconds
- Yellow star fill for favorited units

⌨️ Keyboard Shortcuts:
- "/" - Focus search input
- "Escape" - Close search, blur inputs
- More shortcuts ready to add (Tab, Ctrl+K, etc.)

📦 LocalStorage Utilities (lib/storage.ts):
- saveToHistory() - Add conversion record
- getHistory() - Retrieve history
- clearHistory() - Clear all history
- getFavorites() / addToFavorites() / removeFromFavorites()
- toggleFavorite() - Toggle favorite status
- Type-safe ConversionRecord interface
- Automatic error handling

🎨 Enhanced MainConverter:
- Integrated search at top
- Conversion history at bottom
- Copy & favorite buttons on each result card
- Hover effects with opacity transitions
- Auto-save to history on conversion
- Click history item to restore conversion
- Visual feedback for all interactions

📱 Updated Layout & Page:
- ThemeProvider wraps entire app
- suppressHydrationWarning for SSR
- Top navigation bar with theme toggle
- Keyboard hint for search
- Dark mode gradient text variants

Dependencies Added:
- fuse.js 7.1.0 - Fuzzy search engine
- lucide-react 0.553.0 - Icon library (Search, Copy, Star, Check, etc.)

Features Now Working:
✅ Intelligent fuzzy search across 187 units
✅ Conversion history with persistence
✅ Dark mode with system detection
✅ Copy any result to clipboard
✅ Favorite units for quick access
✅ Keyboard shortcuts (/, Esc)
✅ Smooth animations and transitions
✅ Mobile-responsive design

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

pnpm-lock.yaml

@@ -14,6 +14,12 @@ importers:
       convert-units:
         specifier: ^2.3.4
         version: 2.3.4
+      fuse.js:
+        specifier: ^7.1.0
+        version: 7.1.0
+      lucide-react:
+        specifier: ^0.553.0
+        version: 0.553.0(react@19.2.0)
       next:
         specifier: ^16.0.0
         version: 16.0.1(@babel/core@7.28.5)(react-dom@19.2.0(react@19.2.0))(react@19.2.0)
@@ -1118,6 +1124,10 @@ packages:
   functions-have-names@1.2.3:
     resolution: {integrity: sha512-xckBUXyTIqT97tq2x2AMb+g163b5JFysYk0x4qxNFwbfQkmNZoiRHb6sPzI9/QV33WeuvVYBUIiD4NzNIyqaRQ==}
 
+  fuse.js@7.1.0:
+    resolution: {integrity: sha512-trLf4SzuuUxfusZADLINj+dE8clK1frKdmqiJNb1Es75fmI5oY6X2mxLVUciLLjxqw/xr72Dhy+lER6dGd02FQ==}
+    engines: {node: '>=10'}
+
   generator-function@2.0.1:
     resolution: {integrity: sha512-SFdFmIJi+ybC0vjlHN0ZGVGHc3lgE0DxPAT0djjVg+kjOnSqclqmj0KQ7ykTOLP6YxoqOvuAODGdcHJn+43q3g==}
     engines: {node: '>= 0.4'}
@@ -1530,6 +1540,11 @@ packages:
   lru-cache@5.1.1:
     resolution: {integrity: sha512-KpNARQA3Iwv+jTA0utUVVbrh+Jlrr1Fv0e56GGzAFOXN7dk/FviaDW8LHmK52DlcH4WP2n6gI8vN1aesBFgo9w==}
 
+  lucide-react@0.553.0:
+    resolution: {integrity: sha512-BRgX5zrWmNy/lkVAe0dXBgd7XQdZ3HTf+Hwe3c9WK6dqgnj9h+hxV+MDncM88xDWlCq27+TKvHGE70ViODNILw==}
+    peerDependencies:
+      react: ^16.5.1 || ^17.0.0 || ^18.0.0 || ^19.0.0
+
   magic-string@0.30.21:
     resolution: {integrity: sha512-vd2F4YUyEXKGcLHoq+TEyCjxueSeHnFxyyjNp80yg0XV4vUhnDer/lvvlqM/arB5bXQN5K2/3oinyCRyx8T2CQ==}
 
@@ -3197,6 +3212,8 @@ snapshots:
 
   functions-have-names@1.2.3: {}
 
+  fuse.js@7.1.0: {}
+
   generator-function@2.0.1: {}
 
   gensync@1.0.0-beta.2: {}
@@ -3613,6 +3630,10 @@ snapshots:
     dependencies:
       yallist: 3.1.1
 
+  lucide-react@0.553.0(react@19.2.0):
+    dependencies:
+      react: 19.2.0
+
   magic-string@0.30.21:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.5