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.py

@@ -0,0 +1,60 @@
+"""
+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, Boolean, ForeignKey, JSON, DateTime, Enum
+from sqlalchemy.orm import relationship
+from sqlalchemy.dialects.postgresql import UUID
+from app.database import Base
+import enum
+import uuid
+from datetime import datetime
+
+
+class WorkflowStatus(str, enum.Enum):
+    DRAFT = "draft"
+    PUBLISHED = "published"
+    ARCHIVED = "archived"
+
+
+class Workflow(Base):
+    __tablename__ = "workflows"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String(100), nullable=False)
+    description = Column(Text)
+    status = Column(Enum(WorkflowStatus), default=WorkflowStatus.DRAFT)
+    version = Column(Integer, default=1)
+    is_template = Column(Boolean, default=False)
+    default_language = Column(String(10), default="en")
+    created_at = Column(DateTime, default=datetime.utcnow)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    created_by = Column(UUID(as_uuid=True), ForeignKey("users.id"))
+    organization_id = Column(UUID(as_uuid=True), ForeignKey("organizations.id"))
+    agent_id = Column(UUID(as_uuid=True), ForeignKey("agents.id"))
+    canvas_data = Column(JSON, default={})  # Stores canvas view state (zoom, position)
+    settings = Column(JSON, default={})  # General workflow settings
+
+    # Relationships
+    organization = relationship("Organization", back_populates="workflows")
+    agent = relationship("Agent", foreign_keys=[agent_id], back_populates="workflows")
+    user = relationship("User")
+    nodes = relationship("WorkflowNode", back_populates="workflow", cascade="all, delete-orphan")
+    connections = relationship("WorkflowConnection", back_populates="workflow", cascade="all, delete-orphan")
+
+    sessions = relationship("SessionToAgent", back_populates="workflow")
+
+    class Config:
+        orm_mode = True