feat: écran détail serveur (stats CPU/RAM + image importable RustFS)

- carte cliquable → ServerDetailScreen : bannière (image ou thème), statut,
  connexion/ouvrir, joueurs/MOTD, jauges CPU/RAM/réseau (docker stats),
  import/suppression d'image (galerie → backend → RustFS).
- api_service: stats(), server(), imageBytes(), uploadImage(), deleteImage().
- deps: image_picker.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/screens/servers_screen.dart

@@ -5,6 +5,7 @@ import '../services/api_service.dart';
 import '../services/auth_service.dart';
 import '../services/update_service.dart';
 import '../widgets/server_card.dart';
+import 'server_detail_screen.dart';
 import 'settings_screen.dart';
 
 class ServersScreen extends StatefulWidget {
@@ -110,6 +111,12 @@ class _ServersScreenState extends State<ServersScreen> {
     }
   }
 
+  Future<void> _openDetail(GameServer s) async {
+    await Navigator.push(context,
+        MaterialPageRoute(builder: (_) => ServerDetailScreen(server: s, api: widget.api)));
+    _refresh();
+  }
+
   Future<void> _openSettings() async {
     await Navigator.push(context,
         MaterialPageRoute(builder: (_) => SettingsScreen(api: widget.api)));
@@ -191,6 +198,7 @@ class _ServersScreenState extends State<ServersScreen> {
             iconUrl: snap.data ?? '',
             busy: _busy.contains(s.id),
             onToggle: () => _toggle(s),
+            onTap: () => _openDetail(s),
           ),
         ),
       );