feat: init fitness-coach (backend + miniprogram)

- backend: NestJS service with exercise/plan data
- miniprogram: WeChat mini program client
- exclude node_modules, dist, runtime data-store, local env

miniprogram/components/bottom-nav/index.js

@@ -0,0 +1,20 @@
+Component({
+  properties: {
+    active: { type: String, value: 'home' } // 'home' | 'category' | 'plan'
+  },
+  data: {
+    items: [
+      { key: 'home', label: '首页', emoji: '🏠', page: '/pages/index/index' },
+      { key: 'category', label: '分类', emoji: '📚', page: '/pages/category/category' },
+      { key: 'plan', label: '计划', emoji: '📋', page: '/pages/collection/collection' }
+    ]
+  },
+  methods: {
+    onTap(e) {
+      const page = e.currentTarget.dataset.page;
+      if (!page) return;
+      // 使用 reLaunch 重置页面栈，避免页面层级堆叠
+      wx.reLaunch({ url: page });
+    }
+  }
+});