feat: remove recent conversions functionality from units

- Delete ConversionHistory component
- Remove history-related logic and state from MainConverter
- Clean up history imports and types in CommandPalette and storage utilities
- Remove history storage functions from lib/units/storage.ts

components/units/ui/CommandPalette.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import { useState, useEffect, useCallback, useRef } from 'react';
-import { Command, Hash, Clock, Star, Moon, Sun } from 'lucide-react';
+import { Command, Hash, Star, Moon, Sun } from 'lucide-react';
 import { useTheme } from '@/components/providers/ThemeProvider';
 import {
   getAllMeasures,
@@ -10,7 +10,7 @@ import {
   getCategoryColorHex,
   type Measure,
 } from '@/lib/units/units';
-import { getHistory, getFavorites } from '@/lib/units/storage';
+import { getFavorites } from '@/lib/units/storage';
 import { cn } from '@/lib/utils';
 
 interface CommandPaletteProps {