Add support for .bot files

[jclem]

This adds rudimentary support for .bot files. A .bot file is a .zip archive containing a single file, "bot.json". The JSON currently has the following schema:

z.object({
  version: z.string(),
  model: z.union([z.literal('gpt-3.5-turbo'), z.literal('gpt-4')]),
  systemMessage: z.object({
    type: z.literal('text'),
    content: z.string()
  })
})

An example JSON file for a bot:

{
  "version": "0.0.0",
  "model": "gpt-3.5-turbo",
  "systemMessage": {
    "type": "text",
    "content": "You are a pirate. Talk like one! Use Markdown, though. Ahoy!"
  }
}

To open a .bot file, simply use ⌘+O, or "Open Bot File" from the "File" menu.

Limitations

• No exporting or editing .bot files from within the app, yet.
• The .bot-configured chat will always ignore your app's model setting.
• No changing the .bot-configured chat yet, either. What is opened from the .bot file is currently permanent for that chat.
• No viewing the .bot configuration for a .bot-configured chat.

Bonus

• A terrible "script/bot-icon.mjs" script for generating bot icons (which are not yet supported) from a .bot file.

https://user-images.githubusercontent.com/412282/234438254-c894f609-3048-4e40-ae3c-9c441d2769d6.mp4