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/models/course.py

@@ -223,10 +223,20 @@ class GrowthPath(BaseModel, SoftDeleteMixin):
     target_role: Mapped[Optional[str]] = mapped_column(
         String(100), nullable=True, comment="目标角色"
     )
+    
+    # 岗位关联
+    position_id: Mapped[Optional[int]] = mapped_column(
+        Integer, nullable=True, comment="关联岗位ID"
+    )
 
-    # 路径配置
+    # 路径配置（保留用于兼容，新版使用 nodes 关联表）
     courses: Mapped[Optional[List[dict]]] = mapped_column(
-        JSON, nullable=True, comment="课程列表[{course_id, order, is_required}]"
+        JSON, nullable=True, comment="课程列表[{course_id, order, is_required}]（已废弃，使用nodes）"
+    )
+    
+    # 阶段配置
+    stages: Mapped[Optional[List[dict]]] = mapped_column(
+        JSON, nullable=True, comment="阶段配置[{name, description, order}]"
     )
 
     # 预计时长
@@ -241,6 +251,11 @@ class GrowthPath(BaseModel, SoftDeleteMixin):
     sort_order: Mapped[int] = mapped_column(
         Integer, default=0, nullable=False, comment="排序顺序"
     )
+    
+    # 关联关系
+    nodes: Mapped[List["GrowthPathNode"]] = relationship(
+        "GrowthPathNode", back_populates="growth_path", cascade="all, delete-orphan"
+    )
 
 
 class MaterialKnowledgePoint(BaseModel, SoftDeleteMixin):