fix(telemetry): 将设备信息合并到每个事件的 properties 中上报服务端

设备信息（品牌/型号/OS/版本/语言）此前只存储在本地，对服务端分析毫无价值。
现在在 logEvent() 中将 deviceProps 合并到每个事件的 properties 字段，
使服务端 analytics 表能按设备维度进行统计分析。同时修复 _deviceContext 为
null 时的空指针异常（deviceContextId 使用 ?? '' 安全降级）。
适用于 mining-app 和 mobile-app 两端。

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

frontend/mining-app/lib/core/telemetry/telemetry_service.dart

@@ -179,12 +179,22 @@ class TelemetryService {
       }
     }
 
+    final deviceProps = _deviceContext != null
+        ? {
+            'device_brand': _deviceContext!.brand,
+            'device_model': _deviceContext!.model,
+            'device_os': _deviceContext!.osVersion,
+            'app_version': _deviceContext!.appVersion,
+            'locale': _deviceContext!.locale,
+          }
+        : <String, dynamic>{};
+
     final event = TelemetryEvent(
       eventId: const Uuid().v4(),
       type: type,
       level: level,
       name: eventName,
-      properties: properties,
+      properties: {...deviceProps, ...?properties},
       timestamp: DateTime.now(),
       userId: _userId,
       sessionId: _sessionManager.currentSessionId,

frontend/mobile-app/lib/core/telemetry/telemetry_service.dart

@@ -183,17 +183,27 @@ class TelemetryService {
       }
     }
 
+    final deviceProps = _deviceContext != null
+        ? {
+            'device_brand': _deviceContext!.brand,
+            'device_model': _deviceContext!.model,
+            'device_os': _deviceContext!.osVersion,
+            'app_version': _deviceContext!.appVersion,
+            'locale': _deviceContext!.locale,
+          }
+        : <String, dynamic>{};
+
     final event = TelemetryEvent(
       eventId: const Uuid().v4(),
       type: type,
       level: level,
       name: eventName,
-      properties: properties,
+      properties: {...deviceProps, ...?properties},
       timestamp: DateTime.now(),
       userId: _userId,
       sessionId: _sessionManager.currentSessionId,
       installId: _installId,
-      deviceContextId: _deviceContext!.androidId,
+      deviceContextId: _deviceContext?.androidId ?? '',
     );
 
     _storage.enqueueEvent(event);