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

backend/nest-cli.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "https://json.schemastore.org/nest-cli",
+  "collection": "@nestjs/schematics",
+  "sourceRoot": "src",
+  "compilerOptions": {
+    "deleteOutDir": false,
+    "assets": [
+      { "include": "exercises/data/exercises.json", "outDir": "dist" }
+    ],
+    "watchAssets": true
+  }
+}