Feat: Wire frontend to backend, add wallet API endpoints

- Replace frontend mock with real fetch calls to POST /api/wallet/analyze and GET /api/wallet/{id}/utxos
- Add Vite dev proxy for /api to avoid CORS in development
- Implement WalletResource.java with the two endpoints
- Add WalletMockData.java with the 5-UTXO dataset
- Configure CORS and port in application.properties
- Add backend/requests/wallet.http with kulala tests (29 assertions, all passing)

frontend/src/services/walletService.js

@@ -1,6 +1,13 @@
-import { mockReport } from '../mocks/mockData'
-
 export const analyzeWallet = async (descriptor) => {
-  await new Promise((r) => setTimeout(r, 4000))
-  return mockReport
+  const res1 = await fetch('/api/wallet/analyze', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ descriptor }),
+  })
+  if (!res1.ok) throw new Error('Analysis request failed')
+  const { analysisId } = await res1.json()
+
+  const res2 = await fetch(`/api/wallet/${analysisId}/utxos`)
+  if (!res2.ok) throw new Error('Failed to fetch report')
+  return res2.json()
 }