feat(lagoon): accept string and url rules in lagoon.Validate (quick-261104-f4x)

- string requires a string value (pointers and named string types
  included), url a URL matching Laravel's pattern (urlPattern, shared
  with lagoon.ValidateRequest); both skip an empty or blank value
- lagoon::validate.string and .url in the en and pl catalogs, English
  fallbacks for a nil translator
- settings saves whose model rules use nullable|string|max:255 or
  nullable|url|max:500 no longer fail with an unrecognized-rule error

modules/phrasebook/lang/en/validate.yaml

@@ -11,3 +11,5 @@ max: "The :attribute may not be greater than :max."
 min: "The :attribute must be at least :min."
 oneof: "The selected :attribute is invalid."
 mimes: "The :attribute must be a file of the allowed types."
+string: "The :attribute must be a string."
+url: "The :attribute format is invalid."