fix:Veo3Controller tenant_id를 session 기반으로 변경

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

app/Http/Controllers/Video/Veo3Controller.php

@@ -51,7 +51,7 @@ public function generateTitles(Request $request): JsonResponse
 
         // DB에 pending 레코드 생성
         $video = VideoGeneration::create([
-            'tenant_id' => auth()->user()->tenant_id,
+            'tenant_id' => session('selected_tenant_id'),
             'user_id' => auth()->id(),
             'keyword' => $keyword,
             'status' => VideoGeneration::STATUS_TITLES_GENERATED,