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

.gitignore

@@ -0,0 +1,36 @@
+# OS / editor
+.DS_Store
+Thumbs.db
+*.swp
+*.swo
+
+# dependencies
+node_modules/
+
+# build output
+dist/
+dist-ssr/
+out/
+build/
+
+# runtime data (local JSON "database")
+backend/data-store/
+
+# env / secrets
+.env
+.env.*
+!.env.example
+
+# logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# wechat devtools private config (auto-generated)
+miniprogram/project.private.config.json
+
+# coverage / cache
+coverage/
+.cache/
+.turbo/