新增前后端AI聊天模块，包括流式对话、配置管理和UI组件优化。

backend/app/models.py

@@ -0,0 +1,50 @@
+from datetime import datetime, timezone
+from typing import Optional
+
+from sqlmodel import SQLModel, Field
+
+
+def _now_utc() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+class Novel(SQLModel, table=True):
+    """小说主表"""
+
+    id: Optional[int] = Field(default=None, primary_key=True)
+    title: str = Field(max_length=200, index=True)
+    description: str = Field(default="", max_length=2000)
+    created_at: datetime = Field(default_factory=_now_utc)
+    updated_at: datetime = Field(default_factory=_now_utc)
+
+
+class AIConfig(SQLModel, table=True):
+    """AI服务配置（单行表）"""
+
+    id: Optional[int] = Field(default=None, primary_key=True)
+    provider: str = Field(default="openai")  # "openai" | "anthropic"
+    base_url: str = Field(default="https://api.openai.com/v1")
+    api_key: str = Field(default="")
+    model: str = Field(default="gpt-4o")
+    updated_at: datetime = Field(default_factory=_now_utc)
+
+
+class ChatMessage(SQLModel, table=True):
+    """聊天消息"""
+
+    id: Optional[int] = Field(default=None, primary_key=True)
+    novel_id: Optional[int] = Field(default=None, foreign_key="novel.id", index=True)
+    role: str = Field(max_length=20)  # "user" | "assistant"
+    content: str = Field(default="")
+    created_at: datetime = Field(default_factory=_now_utc)
+
+class Outline(SQLModel, table=True):
+    """大纲表，属于小说的子资源"""
+
+    id: Optional[int] = Field(default=None, primary_key=True)
+    novel_id: int = Field(foreign_key="novel.id", index=True)
+    sort_order: int = Field(default=0)
+    summary: str = Field(max_length=200)
+    detail: str = Field(default="", max_length=1000)
+    created_at: datetime = Field(default_factory=_now_utc)
+    updated_at: datetime = Field(default_factory=_now_utc)