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_102.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u0b85\u0ba9\u0bc8\u0ba4\u0bcd\u0ba4\u0bc8\
 break A}if("keyboardToolbar.done"===e){y="\u0bae\u0bc1\u0b9f\u0bbf\u0ba8\u0bcd\u0ba4\u0ba4\u0bc1"
 break A}y=null
 break A}return y},
-bqv(d){return new A.aV7(d)},
+bqv(d){return new A.aV6(d)},
 a_Y:function a_Y(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aRp:function aRp(){},
-aV7:function aV7(d){this.a=d},
+aRo:function aRo(){},
+aV6:function aV6(d){this.a=d},
 ac6:function ac6(){}}
 B=c[0]
 A=a.updateHolder(c[72],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aRp()}return x},
+x=y.z=new A.aRo()}return x},
 gbe(){return this.r}}
-A.aRp.prototype={
+A.aRo.prototype={
 gbj(){return"\u0bb5\u0bc6\u0b9f\u0bcd\u0b9f\u0bc1"},
 gbi(){return"\u0ba8\u0b95\u0bb2\u0bc6\u0b9f\u0bc1"},
 gbk(){return"\u0b92\u0b9f\u0bcd\u0b9f\u0bc1"},
 gbg(){return"\u0b85\u0ba9\u0bc8\u0ba4\u0bcd\u0ba4\u0bc8\u0baf\u0bc1\u0bae\u0bcd \u0ba4\u0bc7\u0bb0\u0bcd\u0ba8\u0bcd\u0ba4\u0bc6\u0b9f\u0bc1"}}
 A.ac6.prototype={}
 var z=a.updateTypes([])
-A.aV7.prototype={
+A.aV6.prototype={
 $1(d){return A.bpb(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.ac6,B.Z)
 x(A.a_Y,A.ac6)
-x(A.aRp,B.b4)
-x(A.aV7,B.aW)
+x(A.aRo,B.b4)
+x(A.aV6,B.aW)
 y(A.ac6,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"a_Y":{"Z":[]}}'))};
-(a=>{a["Mk6wAxmVHUXM+INAR24Qaj52Jzg="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["n2UAbiIBoRHCyseq3yWeJML1v4o="]=a.current})($__dart_deferred_initializers__);