fix: allow external hostname in vite dev server

Add capakraken.hartmut-noerenberg.com to server.allowedHosts so Vite
does not block requests coming through the reverse proxy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/vite.config.ts

@@ -44,6 +44,7 @@ export default defineConfig({
   server: {
     host: '0.0.0.0',
     port: 5173,
+    allowedHosts: ['capakraken.hartmut-noerenberg.com'],
     proxy: {
       '/api': {
         target: process.env.VITE_API_URL || 'http://localhost:8888',