feat(frontend): add account name editing functionality

- Add AccountUpdate interface to TypeScript types
- Add updateAccount method to API client for PUT /api/v1/accounts/{id}
- Implement inline editing UI in AccountsOverview component
- Add edit/save/cancel buttons with proper state management
- Handle keyboard shortcuts (Enter to save, Escape to cancel)
- Add loading states and error handling for account updates
- Use React Query mutations for optimistic updates
- Refresh account data after successful updates

This enables users to edit account names directly in the Accounts view
using the new API endpoint that was added in the backend.

frontend/src/types/api.ts

@@ -17,6 +17,10 @@ export interface Account {
   balances: AccountBalance[];
 }
 
+export interface AccountUpdate {
+  name?: string;
+}
+
 export interface RawTransactionData {
   transactionId?: string;
   bookingDate?: string;