Fix field-length saves, student wp-admin access, and empty instructor picker

Three bug fixes for the 1.2.1 section:

- Fixed-size fields (question labels, offering titles/notes/e-transfer
  email, policy titles/slugs) no longer silently fail to save when the
  value exceeds its column length. The REST endpoints reject over-long
  values with a 400, the admin controllers refuse to insert them, and the
  form inputs carry a maxlength so the browser blocks over-long entry.
  Limits are MAX_* constants on the value objects, kept in lockstep with
  the schema columns.

- Students are kept out of wp-admin entirely. New StudentAdminGuard
  redirects front-end-only users (no back-office capability) away from the
  dashboard and hides the admin bar for them, while administrators, studio
  admins, and instructors keep full access.

- The Add/Edit Offering instructor picker now includes WordPress
  administrators when they act as instructors (the default single-account
  setup), so a solo studio owner is selectable instead of the dropdown
  being empty.

composer test (618), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

tests/Unit/Offering/OfferingControllerTest.php

@@ -32,6 +32,8 @@ class OfferingControllerTest extends TestCase
         Functions\when('current_user_can')->justReturn(true);
         Functions\when('get_current_user_id')->justReturn(3);
         Functions\when('get_users')->justReturn([]);
+        // Default single-account setup: admins act as instructors.
+        Functions\when('get_option')->justReturn('1');
         Functions\when('check_admin_referer')->justReturn(true);
         Functions\when('admin_url')->justReturn('admin.php?page=us-offerings');
         Functions\when('add_query_arg')->alias(
@@ -450,6 +452,51 @@ class OfferingControllerTest extends TestCase
         self::assertStringNotContainsString('Edit Offering', $html);
     }
 
+    public function testInstructorPickerIncludesAdministratorsWhenTheyActAsInstructors(): void
+    {
+        // The reported bug: a solo studio owner runs the business from a WordPress
+        // administrator account and teaches through the dynamic capability grant,
+        // so they never hold the us_instructor role. The picker must still list
+        // them, otherwise there is no one to assign a class to.
+        Functions\when('get_option')->justReturn('1');
+
+        $admin               = Mockery::mock(\WP_User::class);
+        $admin->ID           = 3;
+        $admin->display_name = 'Studio Owner';
+
+        $queriedRoles = [];
+        Functions\when('get_users')->alias(static function (array $args) use (&$queriedRoles, $admin): array {
+            $queriedRoles = $args['role__in'];
+            return [$admin];
+        });
+        $this->repository->shouldReceive('findAll')->andReturn([]);
+
+        $html = $this->render();
+
+        self::assertContains('us_instructor', $queriedRoles);
+        self::assertContains('administrator', $queriedRoles);
+        self::assertStringContainsString('Studio Owner', $html);
+        self::assertStringContainsString('<option value="3"', $html);
+    }
+
+    public function testInstructorPickerExcludesAdministratorsWhenGrantDisabled(): void
+    {
+        // With the "admins are instructors" toggle off, an admin is not a teacher,
+        // so only the explicit us_instructor role is queried.
+        Functions\when('get_option')->justReturn('0');
+
+        $queriedRoles = null;
+        Functions\when('get_users')->alias(static function (array $args) use (&$queriedRoles): array {
+            $queriedRoles = $args['role__in'];
+            return [];
+        });
+        $this->repository->shouldReceive('findAll')->andReturn([]);
+
+        $this->render();
+
+        self::assertSame(['us_instructor'], $queriedRoles);
+    }
+
     private function render(): string
     {
         ob_start();