fix(mining): handle avatar URL vs SVG in mining page

frontend/mobile-app/lib/features/mining/presentation/pages/mining_page.dart

@@ -463,14 +463,48 @@ class _MiningPageState extends ConsumerState<MiningPage> {
   }
 
   /// 构建SVG或默认头像
+  /// 注意：_avatarSvg 可能存储的是 URL（用户上传的图片）或 SVG 字符串（随机生成的头像）
   Widget _buildSvgOrDefaultAvatar() {
-    if (_avatarSvg != null) {
-      return SvgPicture.string(
-        _avatarSvg!,
-        width: 80,
-        height: 80,
-        fit: BoxFit.cover,
-      );
+    if (_avatarSvg != null && _avatarSvg!.isNotEmpty) {
+      // 检测是否是 URL（用户上传的头像图片）
+      if (_avatarSvg!.startsWith('http://') || _avatarSvg!.startsWith('https://')) {
+        return Image.network(
+          _avatarSvg!,
+          width: 80,
+          height: 80,
+          fit: BoxFit.cover,
+          loadingBuilder: (context, child, loadingProgress) {
+            if (loadingProgress == null) return child;
+            return const Center(
+              child: SizedBox(
+                width: 24,
+                height: 24,
+                child: CircularProgressIndicator(
+                  strokeWidth: 2,
+                  valueColor: AlwaysStoppedAnimation<Color>(Color(0xFFD4AF37)),
+                ),
+              ),
+            );
+          },
+          errorBuilder: (context, error, stackTrace) {
+            return const Icon(
+              Icons.person,
+              size: 40,
+              color: Color(0xFF8B5A2B),
+            );
+          },
+        );
+      }
+
+      // 检测是否是 SVG 字符串（随机生成的 SVG 头像）
+      if (_avatarSvg!.contains('<svg') || _avatarSvg!.startsWith('<?xml')) {
+        return SvgPicture.string(
+          _avatarSvg!,
+          width: 80,
+          height: 80,
+          fit: BoxFit.cover,
+        );
+      }
     }
     return const Icon(
       Icons.person,