feat: implement backend knowledge management

backend/app/models/knowledge.py

@@ -1,14 +1,29 @@
 from datetime import datetime
-from sqlalchemy import DateTime, Integer, String, Text, func
-from sqlalchemy.orm import Mapped, mapped_column
-from app.db.session import Base
 
-class KnowledgeItem(Base):
+from sqlalchemy import CheckConstraint, DateTime, ForeignKey, Integer, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.session import Base
+from app.models.catalog import Versioned
+
+
+class KnowledgeItem(Versioned, Base):
     __tablename__ = "knowledge_items"
+    __table_args__ = (
+        CheckConstraint(
+            "verification_status IN ('pending', 'verified', 'rejected')",
+            name="ck_knowledge_verification_status",
+        ),
+    )
     id: Mapped[int] = mapped_column(Integer, primary_key=True, index=True)
     title: Mapped[str] = mapped_column(String(250), nullable=False, index=True)
     category: Mapped[str] = mapped_column(String(80), nullable=False, default="未分类")
     content: Mapped[str] = mapped_column(Text, nullable=False)
     source_url: Mapped[str | None] = mapped_column(String(1000), nullable=True)
     verification_status: Mapped[str] = mapped_column(String(30), nullable=False, default="pending")
-    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    source_id: Mapped[int | None] = mapped_column(ForeignKey("sources.id"), index=True)
+    document_id: Mapped[int | None] = mapped_column(ForeignKey("documents.id"), index=True)
+    collected_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    reviewer: Mapped[str | None] = mapped_column(String(100))
+    reviewed_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    verification_notes: Mapped[str | None] = mapped_column(Text)