[BUG] Custom search engine string shows as invalid if having extra parameters

[erazemk]

Environment Information

macOS Version: macOS 26.5.1 Tahoe

sol Version: 2.1.345

Issue Description

When adding a custom search engine, if it uses any & params besides ?q=%s (e.g. DuckDuckGo settings or in my case a Kagi token), then it fails the validation and cannot be used.

Reproduction Steps

1. Paste this into the Custom search engine string box: https://duckduckgo.com/?kz=-1&q=%s
2. It fails

Expected Behavior

The parsing is more lenient to allow for cases like the one above (it's a valid DuckDuckGo URL).

Actual Behavior

Validation failed, so the URL can't be used