fix(frontend): post-review fixes sprint 2

- MitreTechniquePicker: guard sync effect while dropdown open to prevent
  mid-stroke wipe when onChange(null,null) propagates back as null props
- SimulationList: replace window.location.href with navigate() to keep
  TanStack Query cache intact on row click
- SimulationFormPage: simplify redundant ternary on SOC form onSubmit
- SimulationFormPage: remove dead .replace(' ','T') on executed_at
  (backend already returns ISO 8601 with T separator)

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

frontend/src/components/MitreTechniquePicker.tsx

@@ -37,12 +37,16 @@ export function MitreTechniquePicker({
   const debounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
   const containerRef = useRef<HTMLDivElement>(null);
   const listRef = useRef<HTMLUListElement>(null);
+  // True once we've synced the first real techniqueId from props (parent/API load).
+  // After that we stop reacting to null, so keystrokes that emit onChange(null,null)
+  // don't propagate back and wipe the input mid-stroke.
+  const hasHydratedFromProps = useRef(false);
 
-  // Sync display when selection changes from outside (initial load)
   useEffect(() => {
     if (techniqueId && techniqueName) {
       setInputValue(`${techniqueId} — ${techniqueName}`);
-    } else if (!techniqueId) {
+      hasHydratedFromProps.current = true;
+    } else if (!techniqueId && !hasHydratedFromProps.current) {
       setInputValue('');
     }
   }, [techniqueId, techniqueName]);

frontend/src/components/SimulationList.tsx

@@ -1,4 +1,4 @@
-import { Link } from 'react-router-dom';
+import { Link, useNavigate } from 'react-router-dom';
 import { extractApiError } from '@/api/client';
 import { useAuth } from '@/hooks/useAuth';
 import { useEngagementSimulations } from '@/hooks/useSimulations';
@@ -19,6 +19,7 @@ function formatDate(value: string | null): string {
 export function SimulationList({ engagementId }: SimulationListProps): JSX.Element {
   const { data, isLoading, isError, error, refetch } = useEngagementSimulations(engagementId);
   const { canEditEngagements } = useAuth();
+  const navigate = useNavigate();
 
   if (isLoading) return <LoadingState label="Loading simulations…" />;
 
@@ -82,14 +83,13 @@ export function SimulationList({ engagementId }: SimulationListProps): JSX.Eleme
                 key={sim.id}
                 className="border-b border-hairline last:border-0 hover:bg-cloud cursor-pointer"
                 onClick={() =>
-                  (window.location.href = `/engagements/${engagementId}/simulations/${sim.id}/edit`)
+                  navigate(`/engagements/${engagementId}/simulations/${sim.id}/edit`)
                 }
               >
                 <td className="px-xl py-md">
                   <Link
                     to={`/engagements/${engagementId}/simulations/${sim.id}/edit`}
                     className="text-ink font-medium hover:underline"
-                    onClick={(e) => e.stopPropagation()}
                   >
                     {sim.name}
                   </Link>