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_69.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u1787\u17d2\u179a\u17be\u179f\u179a\u17be\
 break A}if("keyboardToolbar.done"===e){y="\u179a\u17bd\u1785\u179a\u17b6\u179b\u17cb"
 break A}y=null
 break A}return y},
-br2(d){return new A.aVF(d)},
+br2(d){return new A.aVE(d)},
 a_t:function a_t(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aQV:function aQV(){},
-aVF:function aVF(d){this.a=d},
+aQU:function aQU(){},
+aVE:function aVE(d){this.a=d},
 abC:function abC(){}}
 B=c[0]
 A=a.updateHolder(c[41],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aQV()}return x},
+x=y.z=new A.aQU()}return x},
 gbe(){return this.r}}
-A.aQV.prototype={
+A.aQU.prototype={
 gbj(){return"\u1780\u17b6\u178f\u17cb"},
 gbi(){return"\u1785\u1798\u17d2\u179b\u1784"},
 gbk(){return"\u1794\u17b7\u1791\u1797\u17d2\u1787\u17b6\u1794\u17cb"},
 gbg(){return"\u1787\u17d2\u179a\u17be\u179f\u179a\u17be\u179f\u1791\u17b6\u17c6\u1784\u17a2\u179f\u17cb"}}
 A.abC.prototype={}
 var z=a.updateTypes([])
-A.aVF.prototype={
+A.aVE.prototype={
 $1(d){return A.bpJ(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.abC,B.Z)
 x(A.a_t,A.abC)
-x(A.aQV,B.b4)
-x(A.aVF,B.aW)
+x(A.aQU,B.b4)
+x(A.aVE,B.aW)
 y(A.abC,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"a_t":{"Z":[]}}'))};
-(a=>{a["juFmSlK9ZnekjZWzCQxvyPrVbpc="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["KUnwB3150SFGmoOpk3KPXi+Vi7E="]=a.current})($__dart_deferred_initializers__);