Fix form submission staying in draft status

When no active approval workflow exists, ApprovalService::submit() was
silently returning, leaving the request in Draft while showing a false
success message. Now throws a RuntimeException as a safety net, and the
Livewire component guards before creating any records and shows a clear
error to the user.

app/Services/ApprovalService.php

@@ -17,7 +17,7 @@ class ApprovalService
         $workflow = $travelRequest->workflow;
 
         if (! $workflow) {
-            return;
+            throw new \RuntimeException('No active approval workflow is configured.');
         }
 
         $steps = $workflow->steps()->orderBy('order')->get();