feat(watch): clôture lot #91 - fréquence cardiaque live, notifications de séance et finitions montre

Consolide le lot applicatif watch companion validé :
- télémétrie fréquence cardiaque live remontée montre -> téléphone
  (collecteur watch, adapter Wear Data Layer, persistance Drift,
  propagation aux écrans historique/programme/profil/exécution)
- notifications de séance en arrière-plan côté téléphone (service
  foreground de statut + passerelle applicative)
- finitions montre : chrono d'étape, score d'étape, retrait du bouton
  "lancer une séance", thème, icônes et polices watch_app

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

lib/infrastructure/remote/http_api_client.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 import 'dart:convert';
+import 'dart:io';
 
 import 'package:http/http.dart' as http;
 
@@ -12,11 +13,28 @@ final class HttpApiClient {
     this.timeout = const Duration(seconds: 10),
   }) : client = client ?? http.Client();
 
-  static const defaultBaseUrl = String.fromEnvironment(
+  static const _configuredBaseUrl = String.fromEnvironment(
     'GAMETIME_API_BASE_URL',
-    defaultValue: 'http://localhost:8080',
+    defaultValue: '',
   );
 
+  static String get defaultBaseUrl =>
+      defaultBaseUrlFor(isAndroid: Platform.isAndroid);
+
+  static String defaultBaseUrlFor({
+    required bool isAndroid,
+    String configuredBaseUrl = _configuredBaseUrl,
+  }) {
+    final configured = configuredBaseUrl.trim();
+    if (configured.isNotEmpty) {
+      return configured;
+    }
+    if (isAndroid) {
+      return 'http://10.0.2.2:8080';
+    }
+    return 'http://localhost:8080';
+  }
+
   final Uri baseUrl;
   final http.Client client;
   final Duration timeout;
@@ -142,7 +160,7 @@ final class HttpApiClient {
     return switch (statusCode) {
       401 => RemoteAuthException(RemoteAuthFailure.invalidCredentials, message),
       409 => RemoteAuthException(RemoteAuthFailure.emailAlreadyUsed, message),
-      >= 500 => RemoteAuthException(RemoteAuthFailure.network, message),
+      >= 500 => RemoteAuthException(RemoteAuthFailure.server, message),
       _ => RemoteAuthException(RemoteAuthFailure.unknown, message),
     };
   }