feat(users): allow setting default library access for new users

Add configuration settings and backend support to define default library access permissions for newly created users. Newly registered users automatically receive these default library access permissions upon creation. Also align current users page controls and magic link options in the admin tab settings UI, adding styled callout cards for empty states.

Closes #486

packages/types/src/library.ts

@@ -104,3 +104,7 @@ export interface LibraryAccessEntry {
   name: string;
   accessLevel: AccessLevel;
 }
+
+export interface DefaultLibraryAccessConfig {
+  libraryIds: number[];
+}