feat: establish teaching feedback mini program

Connect student profiles, defaults, and feedback records to the Rust API. Configure the WeChat AppID, custom tab bar, and local development workflow for version 0.1.0.

pages/defaults/index.wxml

@@ -0,0 +1,58 @@
+<view class="page-shell defaults-page">
+  <view class="top-row">
+    <view>
+      <text class="eyebrow">档案预设</text>
+      <view class="page-heading">
+        <text class="heading-icon">＋</text>
+        <text class="page-title">学生档案预设项</text>
+      </view>
+      <text class="page-subtitle">用于新增学生时自动带出</text>
+    </view>
+    <button class="reload-button secondary-button" loading="{{loading}}" disabled="{{loading}}" bindtap="onReload">↻ 刷新</button>
+  </view>
+
+  <view wx:if="{{errorMessage}}" class="status-banner">
+    <text>{{errorMessage}}</text>
+    <text class="status-action" bindtap="onReload">重试</text>
+  </view>
+
+  <view class="defaults-card surface">
+    <view class="defaults-grid">
+      <picker class="select-field" mode="selector" range="{{grades}}" bindchange="onGradeChange">
+        <text class="field-label">年级</text>
+        <text class="field-value">{{defaults.grade}}</text>
+      </picker>
+      <picker class="select-field" mode="selector" range="{{subjects}}" bindchange="onSubjectChange">
+        <text class="field-label">学科</text>
+        <text class="field-value">{{defaults.subject}}</text>
+      </picker>
+    </view>
+
+    <view class="duration-field">
+      <text class="field-label">上课时长</text>
+      <view class="duration-input-row">
+        <input class="duration-input" type="number" value="{{defaults.lessonDurationMinutes}}" bindblur="onDurationInput" />
+        <text class="duration-unit">分钟</text>
+      </view>
+      <slider
+        class="duration-slider"
+        min="15"
+        max="360"
+        step="15"
+        value="{{defaults.lessonDurationMinutes}}"
+        activeColor="#2B67E8"
+        backgroundColor="#DBE7F5"
+        blockColor="#2B67E8"
+        blockSize="26"
+        bindchange="onDurationChange"
+      />
+      <view class="duration-bounds">
+        <text>15 分钟</text>
+        <text>360 分钟</text>
+      </view>
+    </view>
+
+    <view class="time-help">新增学生时会按开始时间自动推算结束时间。</view>
+    <button class="save-defaults primary-button" loading="{{saving}}" disabled="{{saving || loading}}" bindtap="save">保存</button>
+  </view>
+</view>