feat: 添加知识库检索功能和改进模型路由错误处理

- 在ChatRequest中添加Citation事件类型，支持引用来源展示
- 实现聊天上下文准备服务，构建带源元数据的受限聊天上下文
- 添加ThreadedProcess类以支持Windows平台的子进程操作
- 改进检索引擎中的错误处理和向量搜索逻辑
- 实现严格的嵌入模型验证和索引重建机制
- 添加前端聊天界面的知识库检索开关
- 实现搜索历史记录功能和错误降级处理
- 更新模型路由设置提示信息以反映索引重建需求

backend/app/local_models/process.py

@@ -0,0 +1,65 @@
+"""Pipe adapter for event loops without asyncio subprocess support (Windows reload)."""
+from __future__ import annotations
+
+import asyncio
+import subprocess
+
+
+class _Input:
+    def __init__(self, pipe):
+        self.pipe = pipe
+        self.pending = bytearray()
+
+    def write(self, data):
+        self.pending.extend(data)
+
+    async def drain(self):
+        data = bytes(self.pending)
+        self.pending.clear()
+
+        def send():
+            self.pipe.write(data)
+            self.pipe.flush()
+
+        await asyncio.to_thread(send)
+
+    def close(self):
+        self.pipe.close()
+
+
+class _Output:
+    def __init__(self, pipe, limit):
+        self.pipe = pipe
+        self.limit = limit
+
+    async def readline(self):
+        # Bound allocations even when the worker produces a malformed line.
+        return await asyncio.to_thread(self.pipe.readline, self.limit + 1)
+
+
+class ThreadedProcess:
+    def __init__(self, args, *, env, limit, creationflags=0):
+        # Spawn synchronously so cancellation cannot leave an unowned process.
+        # Blocking pipe I/O and reaping run in threads, never on the server loop.
+        self.process = subprocess.Popen(
+            args, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+            stderr=subprocess.DEVNULL, env=env, creationflags=creationflags,
+        )
+        self.stdin = _Input(self.process.stdin)
+        self.stdout = _Output(self.process.stdout, limit)
+
+    @property
+    def returncode(self):
+        return self.process.poll()
+
+    def kill(self):
+        self.process.kill()
+
+    async def wait(self):
+        return await asyncio.to_thread(self.process.wait)
+
+    async def close(self):
+        def close_pipes():
+            self.process.stdin.close()
+            self.process.stdout.close()
+        await asyncio.to_thread(close_pipes)