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/workflow_connection.py

@@ -0,0 +1,45 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+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, Text, ForeignKey, JSON, DateTime
+from sqlalchemy.orm import relationship
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.sql import func
+from app.database import Base
+import uuid
+
+
+class WorkflowConnection(Base):
+    __tablename__ = "workflow_connections"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    workflow_id = Column(UUID(as_uuid=True), ForeignKey("workflows.id", ondelete="CASCADE"), nullable=False)
+    source_node_id = Column(UUID(as_uuid=True), ForeignKey("workflow_nodes.id", ondelete="CASCADE"), nullable=False)
+    target_node_id = Column(UUID(as_uuid=True), ForeignKey("workflow_nodes.id", ondelete="CASCADE"), nullable=False)
+    label = Column(String(100))  # Optional label for the connection
+    condition = Column(Text)  # Optional condition for conditional routing
+    priority = Column(Integer, default=0)  # Priority for multiple outgoing connections
+    connection_metadata = Column(JSON, default={})  # Additional connection properties
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
+
+    # Relationships
+    workflow = relationship("Workflow", back_populates="connections")
+    source_node = relationship("WorkflowNode", foreign_keys=[source_node_id], back_populates="outgoing_connections")
+    target_node = relationship("WorkflowNode", foreign_keys=[target_node_id], back_populates="incoming_connections")
+
+    class Config:
+        orm_mode = True