refactor: migrate LLM helper to agent module and add unified LLM API endpoints

- Move LLMHelper and related logic from app.helper.llm to app.agent.llm.helper
- Update all imports to reference new LLMHelper location
- Introduce app/agent/llm/__init__.py for internal LLM adapter exports
- Add llm.py API router with endpoints for model listing, provider auth, and test calls
- Remove legacy LLM endpoints from system.py
- Update requirements for langchain-anthropic and anthropic
- Refactor test_llm_helper_testcall.py for async LLMHelper usage and new import paths

app/chain/message.py

@@ -21,7 +21,7 @@ from app.chain.transfer import TransferChain
 from app.core.config import settings, global_vars
 from app.db.models import TransferHistory
 from app.db.transferhistory_oper import TransferHistoryOper
-from app.helper.llm import LLMHelper
+from app.agent.llm import LLMHelper
 from app.helper.voice import VoiceHelper
 from app.log import logger
 from app.schemas import Notification, CommingMessage