ui: 暗色金融风重构 + 自定义货币选择器

- 深色主题：深蓝背景 + 毛玻璃卡片 + 金色结果数字
- 自定义底部弹窗货币选择器，替换原生白色 Picker
- 换算卡片内容居中竖排布局
- 汇率信息条改为竖排独立卡片
- 实时脉冲徽章 + 蓝紫渐变互换按钮

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

miniprogram/components/currency-picker/currency-picker.js

@@ -0,0 +1,24 @@
+Component({
+  properties: {
+    show: { type: Boolean, value: false },
+    list: { type: Array, value: [] },
+    current: { type: Number, value: 0 },
+  },
+
+  methods: {
+    handleSelect(e) {
+      const index = e.currentTarget.dataset.index;
+      this.triggerEvent('select', { value: index });
+    },
+
+    handleClose() {
+      this.triggerEvent('close');
+    },
+
+    handleMaskTap() {
+      this.triggerEvent('close');
+    },
+
+    preventBubble() {},
+  },
+});