Refactor: split services.py into services/ package

ChatService → services/chat.py
DocumentService → services/document.py
TTSService → services/tts.py
services/__init__.py re-exports all three for backward-compatible imports

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/chat.py

@@ -0,0 +1,26 @@
+from typing import AsyncIterator
+
+from api_client import APIClientProtocol
+
+
+class ChatService:
+    def __init__(self, api_client: APIClientProtocol):
+        self._api = api_client
+
+    def chat(
+        self, message: str, user_id: str, show_thinking: bool
+    ) -> AsyncIterator[tuple[str, str | None]]:
+        return self._api.chat(message, user_id, show_thinking)
+
+    async def reset(self, user_id: str) -> None:
+        await self._api.reset(user_id)
+
+    async def save_feedback(
+        self,
+        user_id: str,
+        user_msg: str,
+        asst_msg: str,
+        rating: int,
+        run_id: str | None,
+    ) -> None:
+        await self._api.save_feedback(user_id, user_msg, asst_msg, rating, run_id)