细节优化

backend/app/models/document.py

@@ -126,6 +126,11 @@ class Document(UUIDPrimaryKeyMixin, TimestampMixin, Base):
         nullable=False,
         comment="状态 (PENDING/PROCESSING/READY/FAILED/DELETED)",
     )
+    deleted_at: Mapped[str | None] = mapped_column(
+        String(32),
+        nullable=True,
+        comment="进入回收站时间（NULL=未删除），3 天后自动清理",
+    )
     error_code: Mapped[str | None] = mapped_column(
         String(64),
         nullable=True,

backend/app/models/document_category.py

@@ -52,6 +52,11 @@ class DocumentCategory(UUIDPrimaryKeyMixin, TimestampMixin, Base):
         nullable=False,
         comment="排序序号",
     )
+    deleted_at: Mapped[str | None] = mapped_column(
+        String(32),
+        nullable=True,
+        comment="进入回收站时间（NULL=未删除），3 天后自动清理",
+    )
 
     # 关系
     knowledge_base = relationship("KnowledgeBase", back_populates="categories", lazy="selectin")

backend/app/models/knowledge_base.py

@@ -65,6 +65,11 @@ class KnowledgeBase(UUIDPrimaryKeyMixin, TimestampMixin, Base):
         nullable=True,
         comment="链接过期时间，NULL=长期有效",
     )
+    deleted_at: Mapped[str | None] = mapped_column(
+        String(32),
+        nullable=True,
+        comment="进入回收站时间（NULL=未删除），3 天后自动清理",
+    )
 
     # 关系
     user = relationship("User", back_populates="knowledge_bases", lazy="selectin")