refactor(dashboard,desktop,engine): remove unused imports, props, and locals

Clears the remaining no-unused-vars warnings across the dashboard app and
server, desktop main, and engine sources. Dead React state destructures are
collapsed to setter-only, unused props are underscore-prefixed to preserve
API shape, and unreferenced catch bindings are dropped. No behaviour change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/MilestoneSliceInterviewModal.tsx

@@ -87,11 +87,7 @@ export function MilestoneSliceInterviewModal({
   const trackedLockSessionRef = useRef<string | null>(null);
   const [lockSessionId, setLockSessionId] = useState<string | null>(null);
   const sessionTabId = useMemo(() => getSessionTabId(), []);
-  const {
-    isLockedByOther,
-    takeControl,
-    isLoading: isLockLoading,
-  } = useSessionLock(isOpen ? lockSessionId : null);
+  useSessionLock(isOpen ? lockSessionId : null);
   const {
     activeTabMap,
     broadcastUpdate,