Feature: Add custom API Base URL support

[LarsLarkin]

Hi @crybot,

Thank you for this great plugin. I've added a feature that allows users to specify a custom API Base URL in the settings.

This change makes the plugin compatible with third-party providers like OpenRouter, Groq, and local models via Ollama (which was my personal use case).

What I changed:

• settings.ts / components.ts: Added a new text field for the baseURL and changed the "Model" dropdown to a text field to allow custom model names.
• main.ts: Passed the new baseURL from settings to the generation function.
• flashcards.ts:
  1. Passed the baseURL to the OpenAI constructor.
  2. Updated the model validation logic to allow custom models if a baseURL is present.

The plugin remains fully compatible with the original OpenAI API if the baseURL field is left empty.

I hope you find this contribution useful!

[crybot]

@LarsLarkin Thank you for you contribution. This is something I was planning on doing sooner or later, so it's a very welcome change! I'll test it out today and merge it if everything works.