Add support for OpenAI built-in tools (web_search, code_interpreter)

Document the new tools feature in README, features.md, and providers.md.
Update the `!bai providers` command output to show vision/tools support
consistently for all providers.

Based on #62 by @yeslayla which migrated the OpenAI provider to the
Responses API.

See: https://github.com/etkecc/baibot/pull/62

README.md

@@ -17,7 +17,7 @@ It's influenced by [chaz](https://github.com/arcuru/chaz), but does **not** use
 
 - Supports **different use purposes** (depending on the [☁️ provider](./docs/providers.md) & model):
 
-  - [💬 text-generation](./docs/features.md#-text-generation): communicating with you via text (though certain models may "see" images as well)
+  - [💬 text-generation](./docs/features.md#-text-generation): communicating with you via text (though certain models may "see" images as well). The [OpenAI provider](./docs/providers.md#openai) also supports [🛠️ built-in tools](./docs/features.md#️-built-in-tools-openai-only) (web search, code interpreter)
   - [🦻 speech-to-text](./docs/features.md#-speech-to-text): turning your voice messages into text
   - [🗣️ text-to-speech](./docs/features.md#%EF%B8%8F-text-to-speech): turning bot or users text messages into voice messages
   - [🖌️ image-generation](./docs/features.md#image-generation): creating and editing images based on instructions