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/ai_config.py

@@ -0,0 +1,67 @@
+"""
+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 Boolean, Column, Integer, String, JSON, ForeignKey, DateTime, func, Enum as SQLEnum
+from sqlalchemy.orm import relationship
+from enum import Enum
+from app.database import Base
+from sqlalchemy.dialects.postgresql import UUID
+
+class AIModelType(str, Enum):
+    OPENAI = "OPENAI"
+    ANTHROPIC = "ANTHROPIC"
+    DEEPSEEK = "DEEPSEEK"
+    GOOGLE = "GOOGLE"
+    GOOGLEVERTEX = "GOOGLEVERTEX"
+    GROQ = "GROQ"
+    MISTRAL = "MISTRAL"
+    HUGGINGFACE = "HUGGINGFACE"
+    OLLAMA = "OLLAMA"
+    XAI = "XAI"
+    OPENAI_COMPATIBLE = "OPENAI_COMPATIBLE"
+    REPLYPIER = "REPLYPIER" # own model for enterprise customers
+
+DEFAULT_AI_SETTINGS = {
+    "instructions": [
+        "You are a helpful customer service agent.",
+        "Be concise and professional.",
+        "If you don't know something, say so.",
+        "Always maintain a friendly tone."
+    ],
+    "tools": ["web_search"],
+    "memory": True,
+    "markdown": True
+}
+
+
+class AIConfig(Base):
+    __tablename__ = "ai_configs"
+
+    id = Column(Integer, primary_key=True, index=True)
+    organization_id = Column(UUID(as_uuid=True), ForeignKey(
+        "organizations.id"), nullable=False)
+    model_type = Column(SQLEnum(AIModelType), nullable=False)
+    model_name = Column(String, nullable=False)  # e.g. "gpt-4", "claude-3"
+    encrypted_api_key = Column(String, nullable=False)
+    # For additional model-specific settings
+    settings = Column(JSON, nullable=True, default=DEFAULT_AI_SETTINGS)
+    is_active = Column(Boolean, default=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(),
+                        onupdate=func.now())
+
+    # Relationships
+    organization = relationship("Organization", back_populates="ai_configs")