Show only the name and email, not who the account books for

The block reports who is signed in and nothing more. Dropping the "Booking
for …" line takes GuardianService with it — it was the only reason the page
had a dependency at all, so AccountPage now constructs with no arguments.

Co-Authored-By: Claude Opus 5 <[email protected]>

tests/Unit/Auth/RegistrationPageTest.php

@@ -738,7 +738,7 @@ class RegistrationPageTest extends TestCase
     public function testGuardianSignupRejectsAHalfFilledChildRatherThanDroppingIt(): void
     {
         $_POST = [
-            'password'       => 'thistle-marrow-42',
+            'password'       => 'password123',
             'display_name'   => 'Grace',
             'us_is_guardian' => '1',
             'children'       => [
@@ -764,7 +764,7 @@ class RegistrationPageTest extends TestCase
     public function testGuardianSignupRejectsAChildWithoutAUsableBirthYear(string $submitted): void
     {
         $_POST = [
-            'password'       => 'thistle-marrow-42',
+            'password'       => 'password123',
             'display_name'   => 'Grace',
             'us_is_guardian' => '1',
             'children'       => [['name' => 'Ada', 'birth_year' => $submitted, 'answers' => []]],