fix: add constraint actions to db structure

This commit adds several missing "cascade delete" actions to relationships on database tables. This effectively fixes errors while trying to delete user accounts because of pending child records.

Additionally, the observers for applications and vacancies were removed, since they are now obsolete.

The account deletion system was also refactored.

app/User.php

@@ -21,6 +21,7 @@
 
 namespace App;
 
+use App\Services\AccountSuspensionService;
 use App\Traits\HandlesAccountTokens;
 use Illuminate\Contracts\Auth\MustVerifyEmail;
 use Illuminate\Database\Eloquent\SoftDeletes;
@@ -31,7 +32,7 @@ use Spatie\Permission\Traits\HasRoles;
 
 class User extends Authenticatable implements MustVerifyEmail
 {
-    use UserHasTeams, Notifiable, HasRoles, SoftDeletes, HandlesAccountTokens;
+    use UserHasTeams, Notifiable, HasRoles;
 
     /**
      * The attributes that are mass assignable.
@@ -101,7 +102,15 @@ class User extends Authenticatable implements MustVerifyEmail
 
     // UTILITY LOGIC
 
-    public function isBanned()
+    /**
+     * Checks if a user is banned.
+     *
+     * @deprecated This method is obsolete, as it has been replaced by the suspension service.
+     * @see AccountSuspensionService::isSuspended()
+     *
+     * @return bool Whether the user is banned
+     */
+    public function isBanned(): bool
     {
         return ! $this->bans()->get()->isEmpty();
     }