fix: separate server setup page, fix already-logged-in precondition error

lib/core/router.dart

@@ -2,6 +2,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 import 'package:pyramid/features/auth/login_notifier.dart';
 import 'package:pyramid/features/auth/login_page.dart';
+import 'package:pyramid/features/auth/server_page.dart';
 import 'package:pyramid/features/chat/chat_page.dart';
 import 'package:pyramid/features/rooms/rooms_page.dart';
 import 'package:pyramid/features/settings/settings_page.dart';
@@ -9,16 +10,29 @@ import 'package:pyramid/layout/shell_page.dart';
 
 final routerProvider = Provider<GoRouter>((ref) {
   final isLoggedIn = ref.watch(isLoggedInProvider);
+  final homeserverAsync = ref.watch(homeserverProvider);
+  final hasServer = homeserverAsync.valueOrNull != null;
 
   return GoRouter(
     initialLocation: '/rooms',
     redirect: (context, state) {
-      final loggingIn = state.matchedLocation == '/login';
-      if (!isLoggedIn && !loggingIn) return '/login';
-      if (isLoggedIn && loggingIn) return '/rooms';
+      final loc = state.matchedLocation;
+      final onAuth = loc == '/login' || loc == '/server';
+
+      if (!isLoggedIn) {
+        if (!hasServer && loc != '/server') return '/server';
+        if (hasServer && loc != '/login' && !onAuth) return '/login';
+        return null;
+      }
+
+      if (isLoggedIn && onAuth) return '/rooms';
       return null;
     },
     routes: [
+      GoRoute(
+        path: '/server',
+        builder: (context, state) => const ServerPage(),
+      ),
       GoRoute(
         path: '/login',
         builder: (context, state) => const LoginPage(),