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_36.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u0395\u03c0\u03b9\u03bb\u03bf\u03b3\u03ae
 break A}if("keyboardToolbar.done"===e){y="\u03a4\u03ad\u03bb\u03bf\u03c2"
 break A}y=null
 break A}return y},
-brr(d){return new A.aW3(d)},
+brr(d){return new A.aW2(d)},
 a_6:function a_6(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aQy:function aQy(){},
-aW3:function aW3(d){this.a=d},
+aQx:function aQx(){},
+aW2:function aW2(d){this.a=d},
 abf:function abf(){}}
 B=c[0]
 A=a.updateHolder(c[18],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aQy()}return x},
+x=y.z=new A.aQx()}return x},
 gbe(){return this.r}}
-A.aQy.prototype={
+A.aQx.prototype={
 gbj(){return"\u0391\u03c0\u03bf\u03ba\u03bf\u03c0\u03ae"},
 gbi(){return"\u0391\u03bd\u03c4\u03b9\u03b3\u03c1\u03b1\u03c6\u03ae"},
 gbk(){return"\u0395\u03c0\u03b9\u03ba\u03cc\u03bb\u03bb\u03b7\u03c3\u03b7"},
 gbg(){return"\u0395\u03c0\u03b9\u03bb\u03bf\u03b3\u03ae \u03cc\u03bb\u03c9\u03bd"}}
 A.abf.prototype={}
 var z=a.updateTypes([])
-A.aW3.prototype={
+A.aW2.prototype={
 $1(d){return A.bq7(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.abf,B.Z)
 x(A.a_6,A.abf)
-x(A.aQy,B.b4)
-x(A.aW3,B.aW)
+x(A.aQx,B.b4)
+x(A.aW2,B.aW)
 y(A.abf,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"a_6":{"Z":[]}}'))};
-(a=>{a["0m06a8Rx3VeMsmPkX3NFEIZve7g="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["gZJjDviLpQDD4ykgfP/C3kLXnl4="]=a.current})($__dart_deferred_initializers__);