Model choice sticks, custom providers save API keys correctly

FixedBug Fixes

• Your preferred model and reasoning effort now stay selected when you switch between AI providers and restart NameQuick.
• Custom OpenAI-compatible providers now validate and save API keys correctly. Settings shows the saved key, preserves it if a replacement fails, and prevents requests without a required key after an unsuccessful setup.

You may need to enter an existing custom provider's API key again in Settings → AI.