fix(openrouter): include role in sdk model_construct for min dep compat (#35562)

Fix `_wrap_messages_for_sdk` stripping `role` before `model_construct` —
on `openrouter==0.6.0` (minimum dep), the SDK models don't auto-populate
a default `role`, so `model_dump()` omitted it entirely, causing
`KeyError: 'role'` in pre-release checks.

Author: mdrxy

libs/partners/openrouter/langchain_openrouter/chat_models.py

@@ -969,8 +969,7 @@ def _wrap_messages_for_sdk(
             # Unknown role — pass dict through and hope for the best.
             wrapped.append(msg)
             continue
-        fields = {k: v for k, v in msg.items() if k != "role"}
-        wrapped.append(model_cls.model_construct(**fields))
+        wrapped.append(model_cls.model_construct(**msg))
     return wrapped