[Fix] Auth: Restore Request-Context Model Resolution In Skip-Budget Helper

Merge of #26845 kept the PR's _should_skip_budget_checks helper but lost staging's upgrade to _get_model_from_request_context, so zero-cost models resolved from request headers/query params no longer skipped budget checks. Route the helper through _get_model_from_request_context so this path matches the other 8 model-resolution sites in the file.

litellm/proxy/auth/user_api_key_auth.py

@@ -1907,6 +1907,7 @@ async def _run_centralized_common_checks(
     skip_budget_checks = _should_skip_budget_checks(
         request_data=request_data,
         route=route,
+        request=request,
         llm_router=llm_router,
     )
 
@@ -1988,9 +1989,14 @@ async def _reserve_budget_after_common_checks(
 def _should_skip_budget_checks(
     request_data: dict,
     route: str,
+    request: Optional[Request],
     llm_router: Optional[Any],
 ) -> bool:
-    model = get_model_from_request(request_data, route)
+    model = _get_model_from_request_context(
+        request_data=request_data,
+        route=route,
+        request=request,
+    )
     if model is not None and llm_router is not None:
         return _is_model_cost_zero(model=model, llm_router=llm_router)
     return False