feat: upgrade MiniMax default model to M2.7

- Add MiniMax-M2.7 and MiniMax-M2.7-highspeed to supported models list
- Update docstring to list M2.7 models before M2.5
- Update README/README_CHS model references
- Add unit tests for M2.7 and M2.7-highspeed models
- Keep all previous models as alternatives

tests/test_minimax_provider.py

@@ -155,6 +155,42 @@ class TestMiniMaxProvider(unittest.TestCase):
 class TestMiniMaxProviderModels(unittest.TestCase):
     """Test cases for MiniMax provider model configurations."""
 
+    @patch('sources.llm_provider.OpenAI')
+    @patch.dict(os.environ, {'MINIMAX_API_KEY': 'test-key'})
+    def test_minimax_m27_model(self, mock_openai_class):
+        """Test MiniMax-M2.7 model."""
+        mock_client = MagicMock()
+        mock_openai_class.return_value = mock_client
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock(message=MagicMock(content="Response"))]
+        mock_client.chat.completions.create.return_value = mock_response
+
+        with patch.object(Provider, 'get_api_key', return_value='test-key'):
+            provider = Provider("minimax", "MiniMax-M2.7", is_local=False)
+            history = [{"role": "user", "content": "Hello"}]
+            provider.minimax_fn(history)
+
+            call_kwargs = mock_client.chat.completions.create.call_args[1]
+            self.assertEqual(call_kwargs['model'], "MiniMax-M2.7")
+
+    @patch('sources.llm_provider.OpenAI')
+    @patch.dict(os.environ, {'MINIMAX_API_KEY': 'test-key'})
+    def test_minimax_m27_highspeed_model(self, mock_openai_class):
+        """Test MiniMax-M2.7-highspeed model."""
+        mock_client = MagicMock()
+        mock_openai_class.return_value = mock_client
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock(message=MagicMock(content="Response"))]
+        mock_client.chat.completions.create.return_value = mock_response
+
+        with patch.object(Provider, 'get_api_key', return_value='test-key'):
+            provider = Provider("minimax", "MiniMax-M2.7-highspeed", is_local=False)
+            history = [{"role": "user", "content": "Hello"}]
+            provider.minimax_fn(history)
+
+            call_kwargs = mock_client.chat.completions.create.call_args[1]
+            self.assertEqual(call_kwargs['model'], "MiniMax-M2.7-highspeed")
+
     @patch('sources.llm_provider.OpenAI')
     @patch.dict(os.environ, {'MINIMAX_API_KEY': 'test-key'})
     def test_minimax_m25_model(self, mock_openai_class):