feat: Implement multi-language system (ID/EN) for member dashboard

- Create translation files (locales/id.ts, locales/en.ts)
- Add LanguageContext with useLanguage hook
- Add LanguageToggle component in sidebar
- Default language: Indonesian (ID)
- Translate WalletDialog and TransactionDialog
- Language preference persisted in localStorage
- Type-safe translations with autocomplete

Next: Translate remaining pages (Overview, Wallets, Transactions, Profile)

apps/web/src/components/LanguageToggle.tsx

@@ -0,0 +1,24 @@
+import { useLanguage } from '@/contexts/LanguageContext'
+import { Button } from '@/components/ui/button'
+import { Languages } from 'lucide-react'
+
+export function LanguageToggle() {
+  const { language, setLanguage } = useLanguage()
+
+  const toggleLanguage = () => {
+    setLanguage(language === 'id' ? 'en' : 'id')
+  }
+
+  return (
+    <Button
+      variant="ghost"
+      size="sm"
+      onClick={toggleLanguage}
+      className="gap-2"
+      title={language === 'id' ? 'Switch to English' : 'Ganti ke Bahasa Indonesia'}
+    >
+      <Languages className="h-4 w-4" />
+      <span className="text-xs font-medium">{language === 'id' ? 'ID' : 'EN'}</span>
+    </Button>
+  )
+}