feat: update models and prompts

shiny new model imported.
- gpt-5 for daily use
- o3 for complex questions (with high reasoning effort)

Note: gpt-5 model does not support customized temperature, so it's
removed from the api call parameters

assistant.go

@@ -234,9 +234,9 @@ func handleAssistantConversation(c tele.Context, thread []*tele.Message) error {
 	}
 
 	req := openai.ChatRequest{
-		Model:       openai.ModelGpt41,
+		Model:       openai.ModelGpt5,
 		Messages:    chatReqMsgs,
-		Temperature: lo.ToPtr(0.42),
+		Temperature: nil, // lo.ToPtr(0.42),
 		User:        assistantHashUserId(lastMsg.Sender.ID),
 	}