feat: 实现成长路径功能

- 新增数据库表: growth_path_nodes, user_growth_path_progress, user_node_completions
- 新增 Model: GrowthPathNode, UserGrowthPathProgress, UserNodeCompletion
- 新增 Service: GrowthPathService（管理端CRUD、学员端进度追踪）
- 新增 API: 学员端获取成长路径、管理端CRUD
- 前端学员端从API动态加载成长路径数据
- 更新管理端API接口定义

backend/app/api/v1/__init__.py

@@ -125,5 +125,8 @@ api_router.include_router(speech_router, prefix="/speech", tags=["speech"])
 # recommendation_router 智能推荐路由
 from .endpoints.recommendation import router as recommendation_router
 api_router.include_router(recommendation_router, prefix="/recommendations", tags=["recommendations"])
+# growth_path_router 成长路径路由
+from .endpoints.growth_path import router as growth_path_router
+api_router.include_router(growth_path_router, tags=["growth-path"])
 
 __all__ = ["api_router"]