feat(ai-server): fake responses for development

[y3rsh]

Overview

https://opentrons.atlassian.net/browse/AUTH-935
Provide realistic responses from the API that mimic production. Add 2 additional responses that need error handling.

Fakes available are in the API docs

Test Plan and Hands on Testing

Alter UI call to chat/completion

// opentrons-ai-client/src/molecules/InputPrompt/index.tsx
      const config = {
        url,
        method: 'POST',
        headers,
        data: {
          message: userPrompt,
          history: chatHistory,
          fake: true,
          fake_key: 'pcr',
        },

• Alter UI call and test locally
  https://github.com/user-attachments/assets/2eaf39b2-6ba8-4b0f-a43b-948dc2393816
• normal call still works
• validate error message on using an invalid fake_key

{
    "message": "Validation error",
    "details": [
        {
            "type": "literal_error",
            "loc": [
                "body",
                "fake_key"
            ],
            "msg": "Input should be 'reagent transfer', 'reagent transfer flex', 'pcr', 'pcr flex', 'no markdown' or 'empty reply'",
            "input": "fake_value",
            "ctx": {
                "expected": "'reagent transfer', 'reagent transfer flex', 'pcr', 'pcr flex', 'no markdown' or 'empty reply'"
            }
        }
    ]
}