feat(provider): Add MiniMax AI provider integration

- Add minimax to PROVIDERS lists in gui_2.py and app_controller.py
- Add minimax credentials template in ai_client.py
- Implement _list_minimax_models, _classify_minimax_error, _ensure_minimax_client
- Implement _send_minimax with streaming and reasoning support
- Add minimax to send(), list_models(), reset_session(), get_history_bleed_stats()
- Add unit tests in tests/test_minimax_provider.py

src/gui_2.py

@@ -25,7 +25,7 @@ from src import app_controller
 from pydantic import BaseModel
 from imgui_bundle import imgui, hello_imgui, immapp, imgui_node_editor as ed
 
-PROVIDERS: list[str] = ["gemini", "anthropic", "gemini_cli", "deepseek"]
+PROVIDERS: list[str] = ["gemini", "anthropic", "gemini_cli", "deepseek", "minimax"]
 COMMS_CLAMP_CHARS: int = 300
 
 def hide_tk_root() -> Tk: