fix: address code review findings for bookmark feature (H1–L5)

Fix broken tests (H1), align interface signatures with implementations (H3),
remove dead code (H4), add missing input guard (M1), replace raw $_SESSION
access with SessionStoreInterface (M2), sync update script schema (M4),
use shared getAppBase utility (L2), document fragment stripping (L3),
and apply app- CSS class prefix convention (L5).

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

lib/Repository/User/BookmarkGroupRepositoryInterface.php

@@ -4,10 +4,11 @@ namespace MintyPHP\Repository\User;
 
 interface BookmarkGroupRepositoryInterface
 {
-    /** @return list<array<string, mixed>> */
-    public function listByUser(int $userId): array;
-
-    public function nextGroupSortOrder(int $userId): int;
+    /**
+     * @param array{limit?: int, offset?: int} $options
+     * @return list<array<string, mixed>>
+     */
+    public function listByUser(int $userId, array $options = []): array;
 
     public function countByUser(int $userId): int;