Refactor backend integration and service architecture

- Removed the backend client compatibility wrapper and associated methods to streamline backend integration.
- Updated session management to utilize control plane gateways and runtime configuration providers.
- Adjusted TTS service implementations to remove the EdgeTTS service and simplify service dependencies.
- Enhanced documentation to reflect changes in backend integration and service architecture.
- Updated configuration files to remove deprecated TTS provider options and clarify available settings.

engine/core/history_bridge.py

@@ -5,10 +5,12 @@ from __future__ import annotations
 import asyncio
 import time
 from dataclasses import dataclass
-from typing import Any, Optional
+from typing import Optional
 
 from loguru import logger
 
+from core.ports import ConversationHistoryStore
+
 
 @dataclass
 class _HistoryTranscriptJob:
@@ -29,7 +31,7 @@ class SessionHistoryBridge:
     def __init__(
         self,
         *,
-        history_writer: Any,
+        history_writer: ConversationHistoryStore | None,
         enabled: bool,
         queue_max_size: int,
         retry_max_attempts: int,