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/components/navigation/CommandPalette/CommandPalette.tsx

@@ -62,7 +62,7 @@ export function CommandPalette({
   const { t } = useTranslation();
   const navigate = useNavigate();
   const { haptic } = usePlatform();
-  const { isAdmin } = useAuthStore();
+  const isAdmin = useAuthStore((state) => state.isAdmin);
   const { toggleTheme, isDark } = useTheme();
   const [search, setSearch] = useState('');