Fix PHPStan level 6 errors from CI

- Remove unused AvailabilityRepository/BookingRepository from BookingPage
  and ShortcodeRegistrar (template is a JS shell; no PHP data needed yet)
- Add @param array<string, string> to shortcode render() signatures
- Add @return array<string, mixed> to model toArray() methods
- Fix get_permalink() ?? '' — returns string|false not nullable, use cast
- Remove unused ignoreErrors pattern from phpstan.neon

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

phpstan.neon

@@ -7,5 +7,3 @@ parameters:
         - src
     bootstrapFiles:
         - tests/bootstrap.php
-    ignoreErrors:
-        - '#Unsafe usage of new static\(\)#'

src/Frontend/BookingPage.php

@@ -3,17 +3,13 @@ declare(strict_types=1);
 
 namespace Unsupervised\Schedular\Frontend;
 
-use Unsupervised\Schedular\Data\AvailabilityRepository;
-use Unsupervised\Schedular\Data\BookingRepository;
 use Unsupervised\Schedular\Roles\RoleManager;
 
 class BookingPage
 {
-    public function __construct(
-        private AvailabilityRepository $availability,
-        private BookingRepository $bookings,
-    ) {}
-
+    /**
+     * @param array<string, string> $atts
+     */
     public function render(array $atts): string
     {
         if (! is_user_logged_in()) {

src/Frontend/LoginPage.php

@@ -5,10 +5,13 @@ namespace Unsupervised\Schedular\Frontend;
 
 class LoginPage
 {
+    /**
+     * @param array<string, string> $atts
+     */
     public function render(array $atts): string
     {
         if (is_user_logged_in()) {
-            $redirect = esc_url(get_permalink());
+            $redirect = esc_url((string) get_permalink());
             return sprintf(
                 '<p>%s <a href="%s">%s</a>.</p>',
                 esc_html__('You are already logged in.', 'unsupervised-schedular'),
@@ -18,7 +21,7 @@ class LoginPage
         }
 
         $error    = '';
-        $redirect = sanitize_url(get_permalink() ?? '');
+        $redirect = sanitize_url((string) get_permalink());
 
         if (isset($_POST['us_login']) && check_admin_referer('us_student_login')) {
             $credentials = [

src/Frontend/ShortcodeRegistrar.php

@@ -3,17 +3,14 @@ declare(strict_types=1);
 
 namespace Unsupervised\Schedular\Frontend;
 
-use Unsupervised\Schedular\Data\AvailabilityRepository;
-use Unsupervised\Schedular\Data\BookingRepository;
-
 class ShortcodeRegistrar
 {
     private BookingPage $bookingPage;
     private LoginPage $loginPage;
 
-    public function __construct(AvailabilityRepository $availability, BookingRepository $bookings)
+    public function __construct()
     {
-        $this->bookingPage = new BookingPage($availability, $bookings);
+        $this->bookingPage = new BookingPage();
         $this->loginPage   = new LoginPage();
     }
 

src/Model/AvailabilitySlot.php

@@ -24,6 +24,9 @@ class AvailabilitySlot
         );
     }
 
+    /**
+     * @return array<string, mixed>
+     */
     public function toArray(): array
     {
         return [

src/Model/Lesson.php

@@ -33,6 +33,9 @@ class Lesson
         );
     }
 
+    /**
+     * @return array<string, mixed>
+     */
     public function toArray(): array
     {
         return [

src/Plugin.php

@@ -23,6 +23,6 @@ class Plugin
         (new RoleManager())->register();
         (new AdminMenu($availability, $bookings))->register();
         (new RestRegistrar($availability, $bookings))->register();
-        (new ShortcodeRegistrar($availability, $bookings))->register();
+        (new ShortcodeRegistrar())->register();
     }
 }