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/routers/chat.py

@@ -0,0 +1,132 @@
+import json
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, Depends, Query
+from fastapi.responses import StreamingResponse
+from sqlmodel import Session, select, func
+
+from ..database import get_session, engine
+from ..models import AIConfig, ChatMessage
+from ..schemas import ChatRequest, ChatMessageRead, ChatMessageList
+from ..services.ai_provider import stream_chat
+
+router = APIRouter(prefix="/api/chat", tags=["chat"])
+
+
+@router.post("/stream")
+async def chat_stream(
+    data: ChatRequest,
+    session: Session = Depends(get_session),
+):
+    """SSE 流式对话端点"""
+    config = session.exec(select(AIConfig)).first()
+    if not config or not config.api_key:
+        return StreamingResponse(
+            _error_stream("请先配置AI服务"),
+            media_type="text/event-stream",
+        )
+
+    # 保存用户消息
+    user_msg = data.messages[-1] if data.messages else None
+    if user_msg and user_msg.role == "user":
+        db_msg = ChatMessage(
+            novel_id=data.novel_id,
+            role="user",
+            content=user_msg.content,
+        )
+        session.add(db_msg)
+        session.commit()
+
+    # 构建消息列表
+    messages = [{"role": m.role, "content": m.content} for m in data.messages]
+
+    # 构建上下文摘要（前端展示用）
+    context_preview = [{"role": m["role"], "content": m["content"][:200]} for m in messages]
+
+    async def generate():
+        # 先发送上下文预览
+        yield f"data: {json.dumps({'context': context_preview})}\n\n"
+
+        full_response = ""
+        usage_info = {}
+        try:
+            async for event in stream_chat(config, messages):
+                if event.text:
+                    full_response += event.text
+                    yield f"data: {json.dumps({'content': event.text})}\n\n"
+                if event.usage:
+                    # 累加usage
+                    for k, v in event.usage.items():
+                        if v:
+                            usage_info[k] = usage_info.get(k, 0) + v
+        except Exception as e:
+            yield f"data: {json.dumps({'error': str(e)})}\n\n"
+        finally:
+            # 保存AI回复
+            if full_response:
+                with Session(engine) as s:
+                    ai_msg = ChatMessage(
+                        novel_id=data.novel_id,
+                        role="assistant",
+                        content=full_response,
+                    )
+                    s.add(ai_msg)
+                    s.commit()
+            yield f"data: {json.dumps({'done': True, 'usage': usage_info or None})}\n\n"
+
+    return StreamingResponse(
+        generate(),
+        media_type="text/event-stream",
+        headers={
+            "Cache-Control": "no-cache",
+            "X-Accel-Buffering": "no",
+        },
+    )
+
+
+async def _error_stream(message: str):
+    yield f"data: {json.dumps({'error': message})}\n\n"
+    yield f"data: {json.dumps({'done': True})}\n\n"
+
+
+@router.get("/messages", response_model=ChatMessageList)
+def list_messages(
+    novel_id: int | None = Query(default=None),
+    limit: int = Query(default=50, ge=1, le=200),
+    session: Session = Depends(get_session),
+):
+    query = select(ChatMessage)
+    count_query = select(func.count(ChatMessage.id))
+    if novel_id is not None:
+        query = query.where(ChatMessage.novel_id == novel_id)
+        count_query = count_query.where(ChatMessage.novel_id == novel_id)
+    else:
+        query = query.where(ChatMessage.novel_id.is_(None))  # type: ignore
+        count_query = count_query.where(ChatMessage.novel_id.is_(None))  # type: ignore
+
+    total = session.exec(count_query).one()
+    items = session.exec(
+        query.order_by(ChatMessage.created_at.desc()).limit(limit)
+    ).all()
+    # 返回时按时间正序
+    items = list(reversed(items))
+    return ChatMessageList(
+        items=[ChatMessageRead.model_validate(m, from_attributes=True) for m in items],
+        total=total,
+    )
+
+
+@router.delete("/messages", status_code=204)
+def clear_messages(
+    novel_id: int | None = Query(default=None),
+    session: Session = Depends(get_session),
+):
+    query = select(ChatMessage)
+    if novel_id is not None:
+        query = query.where(ChatMessage.novel_id == novel_id)
+    else:
+        query = query.where(ChatMessage.novel_id.is_(None))  # type: ignore
+    messages = session.exec(query).all()
+    for msg in messages:
+        session.delete(msg)
+    session.commit()