refactor: 清理 litellm 冗余代码并锁定依赖版本

backend/src/services/litellm/__init__.py

@@ -1,5 +0,0 @@
-from __future__ import annotations
-
-from services.litellm.service import LiteLLMService
-
-__all__ = ["LiteLLMService"]

backend/src/services/llm_pricing/__init__.py

@@ -0,0 +1,5 @@
+from __future__ import annotations
+
+from services.llm_pricing.service import LlmPricingService
+
+__all__ = ["LlmPricingService"]

backend/src/services/llm_pricing/service.py

@@ -14,7 +14,7 @@ class PricingTier:
     cache_hit_cost_per_token: float
 
 
-class LiteLLMService:
+class LlmPricingService:
     _pricing_by_model: dict[str, tuple[PricingTier, ...]]
 
     def __init__(self) -> None:
@@ -28,7 +28,6 @@ class LiteLLMService:
             if not isinstance(model, dict):
                 continue
             model_code = str(model.get("model_code", "")).strip().lower()
-            litellm_model = str(model.get("litellm_model", "")).strip().lower()
             raw_tiers = model.get("pricing_tiers")
             if not isinstance(raw_tiers, list) or not raw_tiers:
                 continue
@@ -56,8 +55,6 @@ class LiteLLMService:
             )
             if model_code:
                 pricing_by_model[model_code] = ordered_tiers
-            if litellm_model:
-                pricing_by_model[litellm_model] = ordered_tiers
         return pricing_by_model
 
     def calculate_cost(