Domains project remaining tasks

Now that we're wrapping the Domains project, we've decided to document some of the remaining improvements that can be made to it, for future reference.

Improvements

• Show loading state on the Dashboard screen.
• Optimize "Primary site address" chip colors on the Dashboard screen to account for dark mode (reference).
• Optimize discount colors on the Suggestions screen to account for dark mode (reference).
• Make sure the language used by the Checkout page on the web view matches the one set in the app.
• Display Toast/Snackbar message when the user tries to navigate to a blocked URL on the Checkout web view.
• If the user is purchasing a domain for a site with a paid plan, maybe we should set the new domain as the primary one.

Bugs

• Hide domain expiration date on the Dashboard screen when it's not available.
• Show formatted discount currency on the Suggestions screen (reference).
• #15487.

Tasks

• Review Tracks events and make sure it's aligned with iOS.
• Replace @FeatureInDevelopment annotation with @Feature on SiteDomainsFeatureConfig.

Start by reviewing the unchecked items for the Domains Dashboard, Suggestions screen, and Checkout web view, then inspect issue #15487 and the Tracks-event alignment request. The checklist also names SiteDomainsFeatureConfig and a comparison with iOS. Done means the selected remaining improvements are implemented and the corresponding behavior, dark-mode handling, checkout messaging, and analytics alignment are verified.