feat: 首页和资产页面使用 CoinIcon 显示币种图标

✨ 修改内容：
- 首页 (home_page.dart): 持仓列表使用 CoinIcon 替换 CircleAvatar
- 资产持仓 (holdings_section.dart): 使用 CoinIcon 替换文字显示

🎨 效果：
- 首页：持仓卡片显示真实的币种图标
- 资产页面：持仓列表显示真实的币种图标
- 未找到图标时自动显示币种代码（兜底方案）

- ✅ Flutter Web 构建成功 (23.7s)

flutter_monisuo/build/web/main.dart.js_11.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u0412\u044b\u043b\u0443\u0447\u044b\u0446\
 break A}if("keyboardToolbar.done"===e){y="\u0413\u0430\u0442\u043e\u0432\u0430"
 break A}y=null
 break A}return y},
-brC(d){return new A.aWe(d)},
+brC(d){return new A.aWd(d)},
 ZX:function ZX(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aQo:function aQo(){},
-aWe:function aWe(d){this.a=d},
+aQn:function aQn(){},
+aWd:function aWd(d){this.a=d},
 ab5:function ab5(){}}
 B=c[0]
 A=a.updateHolder(c[8],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aQo()}return x},
+x=y.z=new A.aQn()}return x},
 gbe(){return this.r}}
-A.aQo.prototype={
+A.aQn.prototype={
 gbj(){return"\u0412\u044b\u0440\u0430\u0437\u0430\u0446\u044c"},
 gbi(){return"\u041a\u0430\u043f\u0456\u044f\u0432\u0430\u0446\u044c"},
 gbk(){return"\u0423\u0441\u0442\u0430\u0432\u0456\u0446\u044c"},
 gbg(){return"\u0412\u044b\u043b\u0443\u0447\u044b\u0446\u044c \u0443\u0441\u0451"}}
 A.ab5.prototype={}
 var z=a.updateTypes([])
-A.aWe.prototype={
+A.aWd.prototype={
 $1(d){return A.bqi(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.ab5,B.Z)
 x(A.ZX,A.ab5)
-x(A.aQo,B.b4)
-x(A.aWe,B.aW)
+x(A.aQn,B.b4)
+x(A.aWd,B.aW)
 y(A.ab5,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"ZX":{"Z":[]}}'))};
-(a=>{a["kiwRnesZ2/iPXyBiJbSBivaErlU="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["ZxGFhVIn5w0MCsQH6bVFyEZXqt8="]=a.current})($__dart_deferred_initializers__);