AI provider cards now link to API-key setup tutorials

Setting up the newer AI providers needs an API key from each provider's own console, and figuring out which menu to click was not always obvious. Several customers asked us where to find it.

Each provider card in the admin app now includes a direct link to the tutorial we wrote for exactly that. One click, you land on the step-by-step walkthrough, you copy your key, you paste it back into Termerly. The other provider cards already had this; the gap is now closed.