feat: add multi-currency support to cospend payments

- Add ExchangeRate model for currency conversion tracking
- Implement currency utility functions for formatting and conversion
- Add exchange rates API endpoint with caching and fallback rates
- Update Payment and RecurringPayment models to support multiple currencies
- Enhanced payment forms with currency selection and conversion display
- Update split method selector with better currency handling
- Add currency-aware payment display and balance calculations
- Support for EUR, USD, GBP, and CHF with automatic exchange rate fetching

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/routes/+error.svelte

@@ -88,15 +88,15 @@
       <div class="error-icon">
         {getErrorIcon(status)}
       </div>
-      
+
       <h1 class="error-title">
         {getErrorTitle(status)}
       </h1>
-      
+
       <div class="error-code">
         Fehler {status}
       </div>
-      
+
       <p class="error-description">
         {getErrorDescription(status)}
       </p>
@@ -163,7 +163,7 @@
 
 <style>
   .error-page {
-    min-height: calc(100vh - 4rem);
+    min-height: calc(100vh - 6rem);
     display: flex;
     align-items: center;
     justify-content: center;
@@ -390,4 +390,4 @@
       font-size: 1rem;
     }
   }
-</style>
+</style>