feat: Add wallet balance display and currency formatting

- Implement wallet balance computation and formatting in Navbar.vue, enhancing user experience by displaying wallet balance in both the main navigation and dropdown menu.
- Introduce currency conversion utilities in currency.ts to format wallet balances into EverQuest currency denominations, improving clarity for users.

src/lib/utils/currency.ts

@@ -0,0 +1,76 @@
+/**
+ * EverQuest Currency Conversion
+ * 1 sat = 1 copper
+ * 100 copper = 1 silver
+ * 100 silver = 1 gold  
+ * 100 gold = 1 platinum
+ */
+
+export interface EverQuestCurrency {
+  platinum: number
+  gold: number
+  silver: number
+  copper: number
+}
+
+export function satoshisToEverQuest(satoshis: number): EverQuestCurrency {
+  // Convert satoshis to copper (1 sat = 1 copper)
+  let copper = satoshis
+  
+  // Convert to higher denominations
+  const platinum = Math.floor(copper / 1000000) // 100 gold = 1 platinum
+  copper %= 1000000
+  
+  const gold = Math.floor(copper / 10000) // 100 silver = 1 gold
+  copper %= 10000
+  
+  const silver = Math.floor(copper / 100) // 100 copper = 1 silver
+  copper %= 100
+  
+  return {
+    platinum,
+    gold,
+    silver,
+    copper
+  }
+}
+
+export function formatEverQuestCurrency(currency: EverQuestCurrency): string {
+  const parts: string[] = []
+  
+  if (currency.platinum > 0) {
+    parts.push(`${currency.platinum}p`)
+  }
+  
+  if (currency.gold > 0) {
+    parts.push(`${currency.gold}g`)
+  }
+  
+  if (currency.silver > 0) {
+    parts.push(`${currency.silver}s`)
+  }
+  
+  if (currency.copper > 0) {
+    parts.push(`${currency.copper}c`)
+  }
+  
+  // If no currency, show 0c
+  if (parts.length === 0) {
+    return '0c'
+  }
+  
+  return parts.join(' ')
+}
+
+export function formatWalletBalance(balanceMsat: number): string {
+  // Convert msat to satoshis (1 sat = 1000 msat)
+  const satoshis = Math.floor(balanceMsat / 1000)
+  const currency = satoshisToEverQuest(satoshis)
+  return formatEverQuestCurrency(currency)
+}
+
+// Test examples:
+// 100 sat = 1s (1 silver)
+// 10000 sat = 1g (1 gold) 
+// 1000000 sat = 1p (1 platinum)
+// 1234567 sat = 1p 2g 3s 4c