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>

watch_app/lib/infrastructure/watch_bridge/native_watch_bridge_client.dart

@@ -30,6 +30,8 @@ final class WatchCommandAckEvent {
 abstract interface class NativeWatchBridgeClient {
   Stream<WatchSessionProjection> get projections;
 
+  Stream<WatchSensorSample> get sensorSamples;
+
   Stream<WatchCommandAckEvent> get acks;
 
   Stream<WatchBridgeConnectionEvent> get connectionEvents;
@@ -45,25 +47,28 @@ final class MethodChannelNativeWatchBridgeClient
     implements NativeWatchBridgeClient {
   const MethodChannelNativeWatchBridgeClient({
     MethodChannel methodChannel = const MethodChannel(_methodChannelName),
-    EventChannel projectionChannel = const EventChannel(
-      _projectionChannelName,
+    EventChannel projectionChannel = const EventChannel(_projectionChannelName),
+    EventChannel sensorSampleChannel = const EventChannel(
+      _sensorSampleChannelName,
     ),
     EventChannel ackChannel = const EventChannel(_ackChannelName),
-    EventChannel connectionChannel = const EventChannel(
-      _connectionChannelName,
-    ),
+    EventChannel connectionChannel = const EventChannel(_connectionChannelName),
   }) : _methodChannel = methodChannel,
        _projectionChannel = projectionChannel,
+       _sensorSampleChannel = sensorSampleChannel,
        _ackChannel = ackChannel,
        _connectionChannel = connectionChannel;
 
   static const _methodChannelName = 'gametime.watch_bridge/methods';
   static const _projectionChannelName = 'gametime.watch_bridge/projections';
+  static const _sensorSampleChannelName =
+      'gametime.watch_bridge/sensor_samples';
   static const _ackChannelName = 'gametime.watch_bridge/acks';
   static const _connectionChannelName = 'gametime.watch_bridge/connection';
 
   final MethodChannel _methodChannel;
   final EventChannel _projectionChannel;
+  final EventChannel _sensorSampleChannel;
   final EventChannel _ackChannel;
   final EventChannel _connectionChannel;
 
@@ -77,6 +82,16 @@ final class MethodChannelNativeWatchBridgeClient
         });
   }
 
+  @override
+  Stream<WatchSensorSample> get sensorSamples {
+    return _sensorSampleChannel
+        .receiveBroadcastStream()
+        .where((event) => event is Map)
+        .map((event) {
+          return WatchSensorSample.fromJson(_stringObjectMap(event));
+        });
+  }
+
   @override
   Stream<WatchCommandAckEvent> get acks {
     return _ackChannel
@@ -144,7 +159,11 @@ String? _nullableStringFromJson(Object? value) {
 }
 
 int? _nullableIntFromJson(Object? value) {
-  return value is int ? value : value is num ? value.toInt() : null;
+  return value is int
+      ? value
+      : value is num
+      ? value.toInt()
+      : null;
 }
 
 T _enumFromJson<T extends Enum>(Object? value, List<T> values, T fallback) {