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/Dashboard.tsx

@@ -48,14 +48,15 @@ const RefreshIcon = ({ className = 'w-4 h-4' }: { className?: string }) => (
 
 export default function Dashboard() {
   const { t } = useTranslation();
-  const { user, refreshUser } = useAuthStore();
+  const user = useAuthStore((state) => state.user);
+  const refreshUser = useAuthStore((state) => state.refreshUser);
   const queryClient = useQueryClient();
   const navigate = useNavigate();
   const { formatAmount, currencySymbol, formatPositive } = useCurrency();
   const [trialError, setTrialError] = useState<string | null>(null);
   const { isCompleted: isOnboardingCompleted, complete: completeOnboarding } = useOnboarding();
   const [showOnboarding, setShowOnboarding] = useState(false);
-  const { blockingType } = useBlockingStore();
+  const blockingType = useBlockingStore((state) => state.blockingType);
 
   // Refresh user data on mount
   useEffect(() => {