Change "거래" to "지출"

Update navigation label from "거래" to "지출".

src/components/NavBar.tsx

@@ -10,7 +10,7 @@ const NavBar = () => {
   
   const navItems = [
     { icon: Home, label: '홈', path: '/' },
-    { icon: Calendar, label: '거래', path: '/transactions' },
+    { icon: Calendar, label: '지출', path: '/transactions' },
     { icon: BarChart2, label: '분석', path: '/analytics' },
     { icon: Settings, label: '설정', path: '/settings' },
   ];