Fix setup screen always rejecting valid servers

Dio throws DioException for 4xx responses by default, so a server
returning 401 on /api/auth/status (correct behaviour for an
unauthenticated request) was caught and shown as "Could not reach
server", preventing the URL from ever being saved.

Set validateStatus: (_) => true so any HTTP response (200, 401, 404…)
counts as "reachable". Only actual network failures (no response) now
trigger the error message.

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

lib/screens/setup/setup_screen.dart

@@ -36,16 +36,20 @@ class _SetupScreenState extends ConsumerState<SetupScreen> {
     if (url.endsWith('/')) url = url.substring(0, url.length - 1);
 
     try {
-      final dio = Dio(BaseOptions(connectTimeout: const Duration(seconds: 5)));
+      final dio = Dio(BaseOptions(
+        connectTimeout: const Duration(seconds: 5),
+        // Accept any HTTP status — only network-level failures throw.
+        // A 401 or 200 both mean the server is reachable.
+        validateStatus: (_) => true,
+      ));
       await dio.get('$url/api/auth/status');
-      // 401 is fine — server is reachable
     } on DioException catch (_) {
       setState(() {
         _testing = false;
         _error = 'Could not reach server. Check the URL and try again.';
       });
       return;
-    } catch (e) {
+    } catch (_) {
       setState(() {
         _testing = false;
         _error = 'Could not reach server. Check the URL and try again.';