feat: Add OpenAI-compatible API support to AI Writer operation

[aurkinet]

Adds support for any OpenAI-compatible API to the AI Writer operation, allowing users to use local models, cloud providers, and any service that implements the OpenAI Chat completions API format.

To test :

1. Select "OpenAI Compatible (Custom)" as AI Provider
2. Enter custom endpoint (e.g., https://router.huggingface.co/v1)
3. Provide API key
4. Choose model or enter custom model name (e.g., Qwen/Qwen3-Next-80B-A3B-Instruct:novita)

[NemeZZiZZ]

You can use field AI Model with meta.options: {.., allowOther: true} without any special custom field, so user can enter any desired model that is not hardcoded