feat: enhance agent orchestration, knowledge flow and UI refinements

backend/app/models/skill.py

@@ -9,11 +9,12 @@ class Skill(BaseModel):
     name = Column(String(100), nullable=False, unique=True, index=True)
     description = Column(Text, nullable=True)  # 供 LLM 理解用途
     instructions = Column(Text, nullable=False)  # Agent 执行时的指令模板
-    agent_type = Column(String(50), nullable=False, index=True)  # master/planner/executor/librarian/analyst
+    agent_type = Column(String(50), nullable=False, index=True)  # master/schedule_planner/executor/librarian/analyst
     tools = Column(JSON, default=list)  # 引用的工具名称列表
     required_context = Column(JSON, default=list)  # 需要的前置数据
     output_format = Column(Text, nullable=True)  # 输出格式要求
     visibility = Column(String(20), default="private")  # private/team/market
+    is_builtin = Column(Boolean, default=False, nullable=False)
     team_id = Column(String(36), ForeignKey("users.id"), nullable=True)
     is_active = Column(Boolean, default=True)
     owner_id = Column(String(36), ForeignKey("users.id"), nullable=False)