refactor(mp): CSS 变量主题 + 登录页改造 — UI 优化 Phase 0-2

Phase 0: 建立 design token 体系
- tokens.scss 新增 --tk-pri/--tk-pri-l/--tk-pri-d/--tk-shadow-btn/--tk-shadow-tab
- .doctor-mode 覆盖为靛蓝色系，.elder-mode 非线性放大字号
- variables.scss 新增医生端色彩 + 阴影变量

Phase 1: 组件库 + 页面全局替换
- 75 个页面 SCSS $pri → var(--tk-pri) 全量替换
- 11 个新 UI 组件（PrimaryButton/TabFilter/FormInput/ProgressRing 等）
- 8 个现有组件 SCSS 更新
- 18 个医生端页面 useElderClass → useDoctorClass
- PageHeader 匹配原型 NavBar 规格

Phase 2: 登录页重写
- Logo: 方形+ → 圆形渐变 H
- 登录方式: 纯微信 → 账号密码 + 微信一键登录
- 新增 credentialLogin API + store action
- 字号/间距严格匹配原型 mp-01-login.html

apps/miniprogram/src/components/ui/ProgressRing/index.scss

@@ -0,0 +1,28 @@
+@import '../../../styles/variables.scss';
+
+.progress-ring {
+  position: relative;
+  flex-shrink: 0;
+
+  &__center {
+    position: absolute;
+    inset: 0;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+  }
+
+  &__pct {
+    font-family: Georgia, 'Times New Roman', serif;
+    font-size: var(--tk-font-cap);
+    font-weight: 700;
+    color: var(--tk-pri);
+  }
+
+  &__label {
+    font-family: Georgia, 'Times New Roman', serif;
+    font-size: var(--tk-font-micro);
+    font-weight: 700;
+    color: var(--tk-pri);
+  }
+}

apps/miniprogram/src/components/ui/ProgressRing/index.tsx

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+import React from 'react';
+import { View, Text } from '@tarojs/components';
+import './index.scss';
+
+interface ProgressRingProps {
+  progress: number;
+  size?: 'sm' | 'lg';
+  label?: string;
+  className?: string;
+}
+
+const ProgressRing: React.FC<ProgressRingProps> = ({
+  progress,
+  size = 'sm',
+  label,
+  className = '',
+}) => {
+  const px = size === 'sm' ? 64 : 80;
+  const r = (px / 2) - 4;
+  const circumference = 2 * Math.PI * r;
+  const offset = circumference * (1 - Math.min(progress, 1));
+
+  const cls = ['progress-ring', `progress-ring--${size}`, className].filter(Boolean).join(' ');
+
+  return (
+    <View className={cls} style={{ width: px, height: px }}>
+      <svg width={px} height={px} viewBox={`0 0 ${px} ${px}`}>
+        <circle
+          cx={px / 2} cy={px / 2} r={r}
+          fill='none'
+          stroke='var(--tk-pri-l, #E8E2DC)'
+          strokeWidth={4}
+        />
+        <circle
+          cx={px / 2} cy={px / 2} r={r}
+          fill='none'
+          stroke='var(--tk-pri)'
+          strokeWidth={4}
+          strokeDasharray={circumference}
+          strokeDashoffset={offset}
+          strokeLinecap='round'
+          transform={`rotate(-90 ${px / 2} ${px / 2})`}
+        />
+      </svg>
+      <View className='progress-ring__center'>
+        {label ? (
+          <Text className='progress-ring__label'>{label}</Text>
+        ) : (
+          <Text className='progress-ring__pct'>{Math.round(progress * 100)}%</Text>
+        )}
+      </View>
+    </View>
+  );
+};
+
+export default React.memo(ProgressRing);