Show specific error reason on setup screen connection failure

Instead of a generic "Could not reach server" for all failures, show
the actual cause: SSL cert error, timeout, or the raw connection error
message. This makes it possible to diagnose setup issues on-device
without needing a debugger.

Also extend connect timeout from 5s to 10s.

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

lib/screens/setup/setup_screen.dart

@@ -37,22 +37,32 @@ class _SetupScreenState extends ConsumerState<SetupScreen> {
 
     try {
       final dio = Dio(BaseOptions(
-        connectTimeout: const Duration(seconds: 5),
+        connectTimeout: const Duration(seconds: 10),
         // 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');
-    } on DioException catch (_) {
+    } on DioException catch (e) {
+      final msg = switch (e.type) {
+        DioExceptionType.badCertificate =>
+          'SSL certificate error. If using a self-signed cert, it must be trusted on this device.',
+        DioExceptionType.connectionTimeout ||
+        DioExceptionType.receiveTimeout =>
+          'Connection timed out. The server may be down or unreachable.',
+        DioExceptionType.connectionError =>
+          'Cannot connect: ${e.message ?? "network error"}',
+        _ => 'Error: ${e.message ?? e.type.name}',
+      };
       setState(() {
         _testing = false;
-        _error = 'Could not reach server. Check the URL and try again.';
+        _error = msg;
       });
       return;
-    } catch (_) {
+    } catch (e) {
       setState(() {
         _testing = false;
-        _error = 'Could not reach server. Check the URL and try again.';
+        _error = 'Unexpected error: $e';
       });
       return;
     }