Update `gpt-5-nano` docs code examples to `gpt-5.4-nano`

[reynaldichernando]

Another nano model has came out, and we wanted to use a fast and cheap model for the examples in order for people to quickly get a response from puter

i've listed several places that we should update the gpt-5-nano to gpt-5.4-nano:

• https://docs.puter.com/AI/
• https://docs.puter.com/
• https://docs.puter.com/AI/chat/
• https://docs.puter.com/playground/
• https://docs.puter.com/playground/ai-chatgpt/

make sure to update the title and comment, anything relevant

outside of this, there might still be some mention of the gpt 5 nano, we shouldn't update it because its still our default model for puter.ai.chat(), but feel free to suggest if there are other places need updating as well