Dev: allow .ts.net hosts so the dev server works behind tailscale serve

vite.config.ts

@@ -16,6 +16,11 @@ const pkg = JSON.parse(readFileSync(new URL('./package.json', import.meta.url),
 generateLearnPages();
 
 export default defineConfig({
+  server: {
+    // Hetzner dev box: fronted by tailscale serve (HTTPS on the tailnet), which
+    // forwards the ts.net Host header — allow it past DNS-rebinding protection.
+    allowedHosts: ['.ts.net'],
+  },
   resolve: {
     alias: {
       '@': fileURLToPath(new URL('./src', import.meta.url)),