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

lib/units/storage.ts

@@ -2,63 +2,7 @@
  * LocalStorage utilities for persisting user data
  */
 
-export interface ConversionRecord {
-  id: string;
-  timestamp: number;
-  from: {
-    value: number;
-    unit: string;
-  };
-  to: {
-    value: number;
-    unit: string;
-  };
-  measure: string;
-}
-
-const HISTORY_KEY = 'units-ui-history';
 const FAVORITES_KEY = 'units-ui-favorites';
-const MAX_HISTORY = 50;
-
-/**
- * Save conversion to history
- */
-export function saveToHistory(record: Omit<ConversionRecord, 'id' | 'timestamp'>): void {
-  if (typeof window === 'undefined') return;
-
-  const history = getHistory();
-  const newRecord: ConversionRecord = {
-    ...record,
-    id: crypto.randomUUID(),
-    timestamp: Date.now(),
-  };
-
-  // Add to beginning and limit size
-  const updated = [newRecord, ...history].slice(0, MAX_HISTORY);
-  localStorage.setItem(HISTORY_KEY, JSON.stringify(updated));
-}
-
-/**
- * Get conversion history
- */
-export function getHistory(): ConversionRecord[] {
-  if (typeof window === 'undefined') return [];
-
-  try {
-    const stored = localStorage.getItem(HISTORY_KEY);
-    return stored ? JSON.parse(stored) : [];
-  } catch {
-    return [];
-  }
-}
-
-/**
- * Clear conversion history
- */
-export function clearHistory(): void {
-  if (typeof window === 'undefined') return;
-  localStorage.removeItem(HISTORY_KEY);
-}
 
 /**
  * Get favorite units