feat: implement Phase 2 - Core conversion engine and UI

Complete Phase 2 implementation with working unit converter:

Core Conversion Engine (lib/units.ts):
- Type-safe wrapper for convert-units library
- Support for all 23 measures with TypeScript types
- getAllMeasures() - Get all available categories
- getUnitsForMeasure() - Get units for specific measure
- getUnitInfo() - Get detailed unit information
- convertUnit() - Convert between two units
- convertToAll() - Convert to all compatible units
- getCategoryColor() - Get Tailwind color class for measure
- formatMeasureName() - Format measure names for display
- searchUnits() - Fuzzy search across all units

Utility Functions (lib/utils.ts):
- cn() - Merge Tailwind classes with clsx and tailwind-merge
- formatNumber() - Smart number formatting with scientific notation
- debounce() - Debounce helper for inputs
- parseNumberInput() - Parse user input to number
- getRelativeTime() - Format timestamps

UI Components:
- Input - Styled input with focus states
- Button - 6 variants (default, destructive, outline, secondary, ghost, link)
- Card - Card container with header, title, description, content, footer

Main Converter Component (components/converter/MainConverter.tsx):
- Real-time conversion as user types
- Category selection with 23 color-coded buttons
- Input field with unit selector
- Grid display of all conversions in selected measure
- Color-coded result cards with category colors
- Responsive layout (1/2/3 column grid)

Homepage Updates:
- Integrated MainConverter component
- Clean header with gradient text
- Uses design system colors

Dependencies Added:
- clsx - Class name utilities
- tailwind-merge - Merge Tailwind classes intelligently

Features Working:
✓ Select from 23 measurement categories
✓ Real-time conversion to all compatible units
✓ Color-coded categories
✓ Formatted number display
✓ Responsive design

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

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

pnpm-lock.yaml

@@ -8,6 +8,9 @@ importers:
 
   .:
     dependencies:
+      clsx:
+        specifier: ^2.1.1
+        version: 2.1.1
       convert-units:
         specifier: ^2.3.4
         version: 2.3.4
@@ -20,6 +23,9 @@ importers:
       react-dom:
         specifier: ^19.0.0
         version: 19.2.0(react@19.2.0)
+      tailwind-merge:
+        specifier: ^3.3.1
+        version: 3.3.1
     devDependencies:
       '@tailwindcss/postcss':
         specifier: ^4.1.17
@@ -802,6 +808,10 @@ packages:
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+  clsx@2.1.1:
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+    engines: {node: '>=6'}
+
   color-convert@2.0.1:
     resolution: {integrity: sha512-RRECPsj7iu/xb5oKYcsFHSppFNnsj/52OVTRKb4zP5onXwVF3zVmmToNcOfGC+CRDpfK/U584fMg38ZHCaElKQ==}
     engines: {node: '>=7.0.0'}
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     engines: {node: '>= 0.4'}
 
+  tailwind-merge@3.3.1:
+    resolution: {integrity: sha512-gBXpgUm/3rp1lMZZrM/w7D8GKqshif0zAymAhbCyIt8KMe+0v9DQ7cdYLR4FHH/cKpdTXb+A/tKKU3eolfsI+g==}
+
   tailwindcss@4.1.17:
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@@ -2721,6 +2734,8 @@ snapshots:
 
   client-only@0.0.1: {}
 
+  clsx@2.1.1: {}
+
   color-convert@2.0.1:
     dependencies:
       color-name: 1.1.4
@@ -4001,6 +4016,8 @@ snapshots:
 
   supports-preserve-symlinks-flag@1.0.0: {}
 
+  tailwind-merge@3.3.1: {}
+
   tailwindcss@4.1.17: {}
 
   tapable@2.3.0: {}