fix(frontend): post-QA sprint 2 — i18n + alignment + textarea + action bar layout

- Translate all remaining French strings to English (toasts, buttons, banner)
- Fix UsersAdminPage create-form grid alignment: items-start + self-end on button wrapper
- Change execution_result from TextInput to TextArea (5 rows, multiline)
- Replace split Save RT / Save SOC footers + workflow div with a single sticky
  action bar (Save Red Team | Save SOC | Mark for review | Close | Delete)
- Update Vitest assertions to use English button labels

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

frontend/src/components/SimulationList.tsx

@@ -44,7 +44,7 @@ export function SimulationList({ engagementId }: SimulationListProps): JSX.Eleme
               className="btn-primary"
               data-testid="new-simulation-btn"
             >
-              Nouvelle simulation
+              New simulation
             </Link>
           ) : undefined
         }
@@ -62,7 +62,7 @@ export function SimulationList({ engagementId }: SimulationListProps): JSX.Eleme
             className="btn-primary"
             data-testid="new-simulation-btn"
           >
-            Nouvelle simulation
+            New simulation
           </Link>
         ) : null}
       </div>