feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/models/knowledge.py

@@ -0,0 +1,50 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, func, Enum as SQLEnum
+from sqlalchemy.orm import relationship
+from app.database import Base
+import enum
+from sqlalchemy.dialects.postgresql import UUID
+
+class SourceType(str, enum.Enum):
+    DATABASE = "database"
+    FILE = "file"
+    API = "api"
+    WEBSITE = "website"
+    CUSTOM = "custom"
+
+
+class Knowledge(Base):
+    __tablename__ = "knowledge"
+
+    id = Column(Integer, primary_key=True, index=True)
+    # URL, file path, or connection string
+    source = Column(String, nullable=False)
+    source_type = Column(SQLEnum(SourceType), nullable=False)
+    schema = Column(String)  # JSON schema of the data structure
+    table_name = Column(String)
+    organization_id = Column(UUID(as_uuid=True), ForeignKey(
+        "organizations.id"), nullable=False)
+    created_at = Column(DateTime, server_default=func.now())
+    updated_at = Column(DateTime, server_default=func.now(),
+                        onupdate=func.now())
+
+    # Relationships
+    organization = relationship(
+        "Organization", back_populates="knowledge_sources")
+    agent_links = relationship(
+        "KnowledgeToAgent", back_populates="knowledge", cascade="all, delete-orphan")