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.wxss

@@ -0,0 +1,22 @@
+.bn {
+  position: fixed;
+  left: 0; right: 0; bottom: 0;
+  display: flex;
+  background: rgba(20,26,22,0.92);
+  backdrop-filter: blur(12px);
+  border-top: 1rpx solid var(--line);
+  padding-bottom: env(safe-area-inset-bottom);
+  z-index: 60;
+}
+.bn__item {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  padding: 16rpx 0 14rpx;
+  color: var(--text-3);
+}
+.bn__item--active { color: var(--gold); }
+.bn__emoji { font-size: 40rpx; line-height: 1; }
+.bn__label { font-size: 22rpx; margin-top: 6rpx; }
+.bn__item--active .bn__label { color: var(--gold-2); }