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_50.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u0aac\u0aa7\u0ac1\u0a82 \u0aaa\u0ab8\u0a82
 break A}if("keyboardToolbar.done"===e){y="\u0aa5\u0a88 \u0a97\u0aaf\u0ac1\u0a82"
 break A}y=null
 break A}return y},
-brf(d){return new A.aVS(d)},
+brf(d){return new A.aVR(d)},
 a_h:function a_h(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aQJ:function aQJ(){},
-aVS:function aVS(d){this.a=d},
+aQI:function aQI(){},
+aVR:function aVR(d){this.a=d},
 abq:function abq(){}}
 B=c[0]
 A=a.updateHolder(c[29],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aQJ()}return x},
+x=y.z=new A.aQI()}return x},
 gbe(){return this.r}}
-A.aQJ.prototype={
+A.aQI.prototype={
 gbj(){return"\u0a95\u0abe\u0aaa\u0acb"},
 gbi(){return"\u0a95\u0ac9\u0aaa\u0abf \u0a95\u0ab0\u0acb"},
 gbk(){return"\u0aaa\u0ac7\u0ab8\u0acd\u0a9f \u0a95\u0ab0\u0acb"},
 gbg(){return"\u0aac\u0aa7\u0ac1\u0a82 \u0aaa\u0ab8\u0a82\u0aa6 \u0a95\u0ab0\u0acb"}}
 A.abq.prototype={}
 var z=a.updateTypes([])
-A.aVS.prototype={
+A.aVR.prototype={
 $1(d){return A.bpW(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.abq,B.Z)
 x(A.a_h,A.abq)
-x(A.aQJ,B.b4)
-x(A.aVS,B.aW)
+x(A.aQI,B.b4)
+x(A.aVR,B.aW)
 y(A.abq,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"a_h":{"Z":[]}}'))};
-(a=>{a["Gn1M7bsnPkPUQ7KsbJ39Rcht014="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["4T88DD+6jzJ2zW4ueFhAgJENGZY="]=a.current})($__dart_deferred_initializers__);