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/scripts/ensure-data.mjs

@@ -0,0 +1,33 @@
+/**
+ * prebuild 脚本：确保后端数据集存在。
+ * 若 backend/src/exercises/data/exercises.json 不存在，则从 GitHub 原始数据集下载。
+ */
+import * as fs from 'fs';
+import * as path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const DATA_FILE = path.join(__dirname, '..', 'src', 'exercises', 'data', 'exercises.json');
+const SOURCE =
+  'https://raw.githubusercontent.com/hasaneyldrm/exercises-dataset/main/data/exercises.json';
+
+async function main() {
+  if (fs.existsSync(DATA_FILE)) {
+    console.log('[ensure-data] 数据集已存在，跳过下载。');
+    return;
+  }
+  console.log('[ensure-data] 未找到数据集，开始从 GitHub 下载 ...');
+  fs.mkdirSync(path.dirname(DATA_FILE), { recursive: true });
+
+  const res = await fetch(SOURCE);
+  if (!res.ok) throw new Error(`下载失败: HTTP ${res.status}`);
+  const buf = Buffer.from(await res.arrayBuffer());
+  fs.writeFileSync(DATA_FILE, buf);
+  console.log(`[ensure-data] 已保存数据集 (${(buf.length / 1024 / 1024).toFixed(1)} MB)`);
+}
+
+main().catch((e) => {
+  console.error('[ensure-data] 错误:', e.message);
+  console.error('请手动将 exercises-dataset 的 data/exercises.json 放入 backend/src/exercises/data/');
+  process.exit(1);
+});