perf: add Zustand selectors to prevent cascading re-renders

Replace all bare useAuthStore(), useBlockingStore(), and
useSuccessNotification() calls with individual field selectors.
This prevents components from re-rendering when unrelated store
fields change.

- 21 useAuthStore usages across 20 files: individual selectors
  for 1-2 fields, useShallow for 3+ fields
- 5 useBlockingStore usages: individual selectors
- 2 useSuccessNotification usages: individual selectors

src/pages/Profile.tsx

@@ -61,7 +61,8 @@ const PencilIcon = () => (
 
 export default function Profile() {
   const { t } = useTranslation();
-  const { user, setUser } = useAuthStore();
+  const user = useAuthStore((state) => state.user);
+  const setUser = useAuthStore((state) => state.setUser);
   const queryClient = useQueryClient();
 
   const [email, setEmail] = useState('');