Fix global search array-to-string crashes

[CrazyBoy49z]

Fixes the Array to string conversion seen on /admin/search in host apps with translation groups such as lang/uk/page.php and lang/uk/user.php.

Root cause:

• search providers used bare __('Page'), __('User'), and __('Setting') labels;
• on case-insensitive filesystems these can resolve to translation group arrays;
• SearchRegistry then blindly cast provider values to strings.

Changes:

• use package-namespaced search translations for all search labels and result types;
• normalize custom provider values safely, including localized arrays;
• skip malformed search results instead of casting arrays;
• keep user search working when the host app does not expose a user.show route;
• use primary keys for user detail URLs;
• add regression tests for localized array provider values and malformed results.