feat: add video job cancellation functionality and error tracking in generated videos

Co-authored-by: Copilot <copilot@github.com>

frontend/app/static/style.css

@@ -144,6 +144,10 @@ main {
   padding: 0 1rem;
 }
 
+main:has(.admin-page) {
+  max-width: 1200px;
+}
+
 /* ─── Alerts ───────────────────────────────────────────── */
 .alert {
   padding: 0.75rem 1rem;