feat: add reasoning_effort config to enable LLM thinking mode

nanobot/providers/openai_codex_provider.py

@@ -31,6 +31,7 @@ class OpenAICodexProvider(LLMProvider):
         model: str | None = None,
         max_tokens: int = 4096,
         temperature: float = 0.7,
+        reasoning_effort: str | None = None,
     ) -> LLMResponse:
         model = model or self.default_model
         system_prompt, input_items = _convert_messages(messages)