feat: 器械分类网格化 + 分类页标题防乱码 + 按器械/部位多维度筛选

- 首页『热门器械』由横滑 chips 改为与『按部位浏览』一致的网格
- 分类页 navbar 标题改由本地分类枚举回写，避免外部传入标题乱码
- 分类页新增二级维度多选筛选：器械维度交叉按部位，其余维度交叉按器械
- 后端 exercises.service 支持 equipment/bodyPart 逗号分隔多值 OR 过滤（向后兼容）

miniprogram/pages/category/category.wxml

@@ -2,16 +2,35 @@
   <navbar title="{{title}}" show-back />
 
   <view class="section" style="padding-top: 8rpx;">
-    <scroll-view wx:if="{{values.length}}" scroll-x class="filterbar" style="top: calc({{statusBarHeight}}px + 88rpx);">
-      <chip
-        wx:for="{{values}}"
-        wx:key="value"
-        label="{{item.label}}"
-        value="{{item.value}}"
-        active="{{activeValue === item.value}}"
-        bind:select="onValue" />
-      <view class="filterbar__spacer"></view>
-    </scroll-view>
+    <view wx:if="{{values.length}}" class="filterbar" style="top: calc({{statusBarHeight}}px + 88rpx);">
+      <scroll-view scroll-x class="filterbar__row">
+        <chip
+          wx:for="{{values}}"
+          wx:key="value"
+          label="{{item.label}}"
+          value="{{item.value}}"
+          active="{{activeValue === item.value}}"
+          bind:select="onValue" />
+        <view class="filterbar__spacer"></view>
+      </scroll-view>
+
+      <view wx:if="{{secondaryList.length}}" class="filterbar__sub">
+        <view class="filterbar__subhead">
+          <text class="filterbar__sublabel">{{secondaryLabel}}</text>
+          <text wx:if="{{secondarySelected.length}}" class="filterbar__clear" bindtap="onSecondaryClear">清除 ({{secondarySelected.length}})</text>
+        </view>
+        <scroll-view scroll-x class="filterbar__row">
+          <chip
+            wx:for="{{secondaryList}}"
+            wx:key="value"
+            label="{{item.label}}"
+            value="{{item.value}}"
+            active="{{item.active}}"
+            bind:select="onSecondary" />
+          <view class="filterbar__spacer"></view>
+        </scroll-view>
+      </view>
+    </view>
     <view wx:else class="filterbar__loading muted">{{ loading ? '加载分类中…' : '暂无分类' }}</view>
 
     <view class="count muted" wx:if="{{!loading}}">共 {{total}} 个动作</view>