Grant studio-admin capabilities to WordPress administrators

WordPress administrators (manage_options) now implicitly hold every
studio-admin capability via a user_has_cap filter, so the site owner runs
the studio without being assigned the separate us_studio_admin role. The
grant persists nothing and is removed on deactivation. The us_studio_admin
role still exists for non-administrator staff and does NOT confer any core
WordPress admin powers.

Also re-gate the studio-wide "Scheduler" dashboard off manage_options onto
a new view_all_lessons capability (added to the studio-admin cap set), so a
us_studio_admin user can see it too — previously it was administrator-only.

- RoleManager: STUDIO_ADMIN_CAPS constant, CAP_VIEW_ALL_LESSONS,
  grantStudioCapsToAdministrators() user_has_cap filter
- AdminMenu + LessonController: Scheduler gated on view_all_lessons
- Docs: user-roles.md cap matrix + administrator note; lesson-booking.md
- Tests: administrators receive studio caps; non-admins do not

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Unit/Auth/RoleManagerTest.php

@@ -9,15 +9,36 @@ use Unsupervised\Schedular\Tests\Unit\TestCase;
 
 class RoleManagerTest extends TestCase
 {
-    public function testRegisterAddsInitHook(): void
+    public function testRegisterAddsInitHookAndCapFilter(): void
     {
         Functions\expect('add_action')
             ->once()
             ->with('init', \Mockery::any());
 
+        Functions\expect('add_filter')
+            ->once()
+            ->with('user_has_cap', \Mockery::any(), 10, 1);
+
         (new RoleManager())->register();
     }
 
+    public function testGrantsStudioCapsToAdministrators(): void
+    {
+        $result = (new RoleManager())->grantStudioCapsToAdministrators(['manage_options' => true]);
+
+        foreach (RoleManager::STUDIO_ADMIN_CAPS as $cap) {
+            self::assertTrue($result[$cap], "administrator should be granted {$cap}");
+        }
+    }
+
+    public function testDoesNotGrantStudioCapsToNonAdministrators(): void
+    {
+        $result = (new RoleManager())->grantStudioCapsToAdministrators(['read' => true]);
+
+        self::assertArrayNotHasKey(RoleManager::CAP_MANAGE_OFFERINGS, $result);
+        self::assertSame(['read' => true], $result);
+    }
+
     public function testCreateRolesSkipsExistingRoles(): void
     {
         Functions\when('get_role')->alias(static fn() => new \stdClass());