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_81.part.js

@@ -23,14 +23,14 @@ break A}if("input.selectAll"===e){y="\u1021\u102c\u1038\u101c\u102f\u1036\u1038\
 break A}if("keyboardToolbar.done"===e){y="\u1015\u103c\u102e\u1038\u1015\u103c\u102e"
 break A}y=null
 break A}return y},
-bqQ(d){return new A.aVs(d)},
+bqQ(d){return new A.aVr(d)},
 a_F:function a_F(d,e){var _=this
 _.r=d
 _.z=_.w=$
 _.a=e
 _.e=_.b=$},
-aR6:function aR6(){},
-aVs:function aVs(d){this.a=d},
+aR5:function aR5(){},
+aVr:function aVr(d){this.a=d},
 abO:function abO(){}}
 B=c[0]
 A=a.updateHolder(c[53],A)
@@ -39,22 +39,22 @@ h(d,e){var y=this.r.a7(e)
 return y==null?this.a.a7(e):y},
 gb9(){var y=this,x=y.z
 if(x===$){if(y.w===$)y.w=y
-x=y.z=new A.aR6()}return x},
+x=y.z=new A.aR5()}return x},
 gbe(){return this.r}}
-A.aR6.prototype={
+A.aR5.prototype={
 gbj(){return"\u1016\u103c\u1010\u103a"},
 gbi(){return"\u1019\u102d\u1010\u1039\u1010\u1030\u1000\u1030\u1038"},
 gbk(){return"\u1000\u1030\u1038\u1011\u100a\u1037\u103a"},
 gbg(){return"\u1021\u102c\u1038\u101c\u102f\u1036\u1038\u101b\u103d\u1031\u1038\u1001\u103b\u101a\u103a"}}
 A.abO.prototype={}
 var z=a.updateTypes([])
-A.aVs.prototype={
+A.aVr.prototype={
 $1(d){return A.bpw(this.a,d)},
 $S:2};(function inheritance(){var y=a.mixin,x=a.inherit
 x(A.abO,B.Z)
 x(A.a_F,A.abO)
-x(A.aR6,B.b4)
-x(A.aVs,B.aW)
+x(A.aR5,B.b4)
+x(A.aVr,B.aW)
 y(A.abO,B.b_)})()
 B.b9(b.typeUniverse,JSON.parse('{"a_F":{"Z":[]}}'))};
-(a=>{a["7JxmaV1YCgaJUyRSFfx4CUQKvwI="]=a.current})($__dart_deferred_initializers__);
+(a=>{a["rgp1/FLjuSphdzdeYVIQ9JMP60g="]=a.current})($__dart_deferred_initializers__);