feature request: export and import for provider configurations

[shinohara-rin]

Mostly for DX

It's kinda annoying having to manually fill out all the forms after data purge, which happens a lot during development.

Being able to import settings from a configuration file / env would make working on AIRI more enjoyable.

[leaft]

Using both YAML and .env is a great idea.
We can build a settings page for developers within devtools directory.
Think of it as a developer-friendly take on the data settings page.

[NJX-njx]

I'd like to work on this. Plan: implement JSON-based export/import for provider configurations (API keys, endpoints, model selections). Will add export button to serialize current provider configs to a downloadable JSON file, and an import button with file picker + validation via Valibot schema to restore configurations.