💄 feat: 为个人中心页头像添加默认图标显示

- 移除外部默认头像图片URL，改用图标类显示
- 当用户没有头像时显示用户图标 (i-heroicons-user-circle-20-solid)
- 添加默认头像样式：浅灰色背景、边框、图标居中
- 提升用户体验和加载性能

🤖 Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

mini/src/components/tdesign/user-center-card/index.css

@@ -32,6 +32,15 @@
   overflow: hidden;
 }
 
+/* 默认头像样式 */
+.tdesign-user-center-card__header__avatar--default {
+  background-color: #f5f5f5;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  border: 2rpx solid #e5e5e5;
+}
+
 /* 用户名样式 */
 .tdesign-user-center-card__header__name {
   font-size: 36rpx;

mini/src/components/tdesign/user-center-card/index.tsx

@@ -22,8 +22,6 @@ export default function TDesignUserCenterCard({
   onGetUserInfo,
   className = ''
 }: UserCenterCardProps) {
-  const defaultAvatarUrl = 'https://cdn-we-retail.ym.tencent.com/miniapp/usercenter/icon-user-center-avatar@2x.png'
-
   const handleClick = () => {
     if (isNeedGetUserInfo && onGetUserInfo) {
       onGetUserInfo()
@@ -37,11 +35,17 @@ export default function TDesignUserCenterCard({
       {/* 用户信息头部 */}
       <View className="tdesign-user-center-card__header" onClick={handleClick}>
         {/* 头像 */}
-        <Image
-          src={avatar || defaultAvatarUrl}
-          mode="aspectFill"
-          className="tdesign-user-center-card__header__avatar"
-        />
+        {avatar ? (
+          <Image
+            src={avatar}
+            mode="aspectFill"
+            className="tdesign-user-center-card__header__avatar"
+          />
+        ) : (
+          <View className="tdesign-user-center-card__header__avatar tdesign-user-center-card__header__avatar--default">
+            <View className="i-heroicons-user-circle-20-solid w-full h-full text-gray-400" />
+          </View>
+        )}
 
         {/* 用户名 */}
         <Text className="tdesign-user-center-card__header__name">