fix(registration): resume the right action after the membership-id warning

confirmMembershipSibling() always called nextStep(). With a single-child
wizard that was the only thing it could have been resuming, but the warning is
now reachable from "add another sibling" too — and answering it there jumped
the desk to step 2, throwing away the child they were half way through adding.
It now resumes whichever action raised it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/Livewire/Receptionist/NewRegistrationWizard.php

@@ -88,6 +88,14 @@ class NewRegistrationWizard extends Component
     public string $membership_id = '';
     public bool $membershipIdSiblingConfirmed = false;
     public array $membershipIdSiblings = [];
+
+    /**
+     * What the desk was doing when the membership-id warning interrupted them
+     * — 'add' for "add another sibling", null for "next". Locked: this decides
+     * which handler runs on confirm, and it is set by this component only.
+     */
+    #[Locked]
+    public ?string $membershipSiblingPendingAction = null;
     public string $participant_governorate = '';
     public bool $participant_is_foreign = false;
     public bool $participant_nid_decoded = false;
@@ -333,10 +341,28 @@ private function autoFillGuardianName(): void
         }
     }
 
+    /**
+     * The desk has seen the "this membership id already has players on it"
+     * warning and wants to carry on.
+     *
+     * It resumes whatever was interrupted rather than always advancing:
+     * with a roster, that warning can be raised by "add another sibling" just
+     * as easily as by "next", and forcing the desk on to step 2 would throw
+     * away the child they were half way through adding.
+     */
     public function confirmMembershipSibling(): void
     {
         $this->membershipIdSiblingConfirmed = true;
         $this->membershipIdSiblings = [];
+
+        if ($this->membershipSiblingPendingAction === 'add') {
+            $this->membershipSiblingPendingAction = null;
+            $this->addPlayer();
+
+            return;
+        }
+
+        $this->membershipSiblingPendingAction = null;
         $this->nextStep();
     }
 
@@ -493,7 +519,11 @@ private function membershipSiblingCheckPassed(): bool
     /** Add the child in the draft form and leave the sheet ready for another. */
     public function addPlayer(): void
     {
-        $this->commitDraft();
+        $this->membershipSiblingPendingAction = 'add';
+
+        if ($this->commitDraft()) {
+            $this->membershipSiblingPendingAction = null;
+        }
     }
 
     public function editPlayer(int $index): void