Change default OpenAI model (gpt-4.1 -> gpt-5)

Ref: https://openai.com/index/introducing-gpt-5/

docs/sample-provider-configs/openai.yml

@@ -1,7 +1,7 @@
 base_url: https://api.openai.com/v1
 api_key: YOUR_API_KEY_HERE
 text_generation:
-  model_id: gpt-4.1
+  model_id: gpt-5
   prompt: "You are a brief, but helpful bot called {{ baibot_name }} powered by the {{ baibot_model_id }} model. The date/time of this conversation's start is: {{ baibot_conversation_start_time_utc }}."
   temperature: 1.0
   max_response_tokens: 16384

etc/app/config.yml.dist

@@ -76,7 +76,7 @@ agents:
     #     base_url: https://api.openai.com/v1
     #     api_key: ""
     #     text_generation:
-    #       model_id: gpt-4.1
+    #       model_id: gpt-5
     #       prompt: "You are a brief, but helpful bot called {{ baibot_name }} powered by the {{ baibot_model_id }} model. The date/time of this conversation's start is: {{ baibot_conversation_start_time_utc }}."
     #       temperature: 1.0
     #       max_response_tokens: 16384

src/agent/provider/openai/config.rs

@@ -80,7 +80,7 @@ impl Default for TextGenerationConfig {
 }
 
 fn default_text_model_id() -> String {
-    "gpt-4.1".to_owned()
+    "gpt-5".to_owned()
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]