style: 优化后台整体UI风格与组件样式

1.  新增并配置全局颜色、阴影、圆角等主题变量
2.  统一各页面卡片、表单、按钮等组件的样式规范
3.  优化登录页、个人中心、仪表盘等页面的布局与视觉效果
4.  添加全局滚动条样式与元素过渡动画

tailwind.config.js

@@ -14,6 +14,10 @@ export default {
         canvas: '#f2f3f5',
         panel: '#fbfcfd',
         brand: '#165dff',
+        'brand-light': '#e8f3ff',
+        success: '#00b42a',
+        warning: '#ff7d00',
+        danger: '#f53f3f',
       },
       fontFamily: {
         sans: [
@@ -28,6 +32,11 @@ export default {
       },
       boxShadow: {
         login: '0 18px 48px rgba(15, 23, 42, 0.08)',
+        card: '0 1px 3px rgba(0,0,0,0.04), 0 1px 2px rgba(0,0,0,0.02)',
+        'card-hover': '0 4px 12px rgba(0,0,0,0.08)',
+      },
+      borderRadius: {
+        xl: '0.75rem',
       },
     },
   },