feat: upgrade MiniMax default model to M2.7

- Add MiniMax-M2.7 and MiniMax-M2.7-highspeed to model list
- Set MiniMax-M2.7 as default model
- Keep all previous models as alternatives
- Add unit tests for model configuration

tests-unit/comfy_api_test/minimax_models_test.py

@@ -0,0 +1,27 @@
+import pytest
+from comfy_api_nodes.apis.minimax import MiniMaxChatModel
+
+
+class TestMiniMaxChatModel:
+    def test_m27_in_model_list(self):
+        """MiniMax-M2.7 should be available in the chat model enum."""
+        assert MiniMaxChatModel.M2_7.value == 'MiniMax-M2.7'
+
+    def test_m27_highspeed_in_model_list(self):
+        """MiniMax-M2.7-highspeed should be available in the chat model enum."""
+        assert MiniMaxChatModel.M2_7_highspeed.value == 'MiniMax-M2.7-highspeed'
+
+    def test_m27_is_first_in_enum(self):
+        """M2.7 should appear before older models in the enum."""
+        members = list(MiniMaxChatModel)
+        assert members[0] == MiniMaxChatModel.M2_7
+        assert members[1] == MiniMaxChatModel.M2_7_highspeed
+
+    def test_legacy_models_still_available(self):
+        """Previous M2.5 models should still be available."""
+        assert MiniMaxChatModel.M2_5.value == 'MiniMax-M2.5'
+        assert MiniMaxChatModel.M2_5_highspeed.value == 'MiniMax-M2.5-highspeed'
+
+    def test_total_model_count(self):
+        """Should have 4 chat models total (M2.7, M2.7-highspeed, M2.5, M2.5-highspeed)."""
+        assert len(MiniMaxChatModel) == 4