数据层可插拔(SQLite/MariaDB) + 后端 services 骨架

- database.ts 改为按 DB_TYPE 切换 SQLite / MariaDB(mysql2)，sqlite3 按需动态导入
- index.ts 改为初始化数据库后再监听端口
- 新增 AuthService / HealthService / AnalysisService / GarminService
- 新增 .gitignore、server/.env(忽略) 与 .env.example
- README 增加数据库配置说明；package.json 增加 mysql2/@types

server/package.json

@@ -14,6 +14,7 @@
     "express": "^4.18.2",
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
+    "mysql2": "^3.6.0",
     "sqlite3": "^5.1.6",
     "jsonwebtoken": "^9.0.2",
     "axios": "^1.5.0",
@@ -21,8 +22,10 @@
   },
   "devDependencies": {
     "@types/express": "^4.17.17",
+    "@types/cors": "^2.8.13",
     "@types/node": "^20.3.1",
     "@types/jsonwebtoken": "^9.0.2",
+    "@types/sqlite3": "^3.1.8",
     "typescript": "^5.1.3",
     "tsx": "^3.12.7"
   }