feat: 添加分享按钮图片资源和配置

- 在 Images.xcassets 中创建三个新的 Image Set：
  * shareWechat.imageset - 微信分享按钮图标
  * shareQQ.imageset - QQ分享按钮图标
  * shareDouyin.imageset - 抖音分享按钮图标

- 为每个 Image Set 配置 Contents.json，支持 @1x/@2x/@3x 多倍率
- 增强 SharePanel.m 按钮样式设置，添加可选的边框和阴影效果
- 添加详细的图片添加指南文档：
  * images_xcassets_guide.md - Images.xcassets 使用指南
  * share_button_guide.md - 分享按钮设计规范

图片规格：60×60pt (@1x), 120×120pt (@2x), 180×180pt (@3x)
支持圆形按钮设计，代码自动处理圆角效果

msext/Class/Utils/SharePanel.m

@@ -149,8 +149,21 @@ static SharePanel *sharedPanel = nil;
     CGFloat x = startX + index * (kButtonSize + kButtonMargin);
     button.frame = CGRectMake(x, kButtonTopMargin, kButtonSize, kButtonSize);
     [button setImage:[UIImage imageNamed:imageName] forState:UIControlStateNormal];
+    
+    // 圆角设置
     button.layer.cornerRadius = kButtonSize / 2;
     button.clipsToBounds = YES;
+    
+    // 可选：添加边框效果
+    // button.layer.borderWidth = 1.0;
+    // button.layer.borderColor = [UIColor colorWithWhite:0.9 alpha:1.0].CGColor;
+    
+    // 可选：添加阴影效果（注意：阴影和clipsToBounds冲突，需要使用容器视图）
+    // button.layer.shadowColor = [UIColor blackColor].CGColor;
+    // button.layer.shadowOffset = CGSizeMake(0, 2);
+    // button.layer.shadowOpacity = 0.1;
+    // button.layer.shadowRadius = 4;
+    
     return button;
 }
 

msext/Images.xcassets/shareDouyin.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "shareDouyin.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "shareDouyin@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "shareDouyin@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

msext/Images.xcassets/shareQQ.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "shareQQ.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "shareQQ@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "shareQQ@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

msext/Images.xcassets/shareWechat.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "shareWechat.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "shareWechat@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "shareWechat@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}