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/pages/index/index.json

@@ -0,0 +1,8 @@
+{
+  "navigationStyle": "custom",
+  "usingComponents": {
+    "exercise-card": "/components/exercise-card/index",
+    "section-header": "/components/section-header/index",
+    "bottom-nav": "/components/bottom-nav/index"
+  }
+}