fix: react-doctor → 64/100 (Bugs 122, Perf 286, A11y 613, Maint 436)

- CartContext: lazy initializers replace mount-only useEffect
  hydration; remove 8 no-initialize-state warnings
- Toast/AdminSearchInput: React 19 useContext/use + drop
  forwardRef (3 no-react19-deprecated-apis)
- ProductFormModal: lazy initializers + useSyncExternalStore
  for mount; parent adds key=editingProduct.id
- InstallPrompt: useReducer for prompt state (no-cascading-set-state)
- QRScanModal: ref-based latest-callback pattern replaces
  useEffectEvent deps mistake
- OnboardingFlow: functional setState (rerender-functional-setstate)
- UsersPage/StopsCalendar/FeaturesAndStats: lazy initializers
  (rerender-lazy-state-init)
- FAQClientPage: server-side brand settings fetch via getBrandSettingsPublic
  in layout; remove supabase import
- LandingPageWrapper: href='#' → href='#top' (anchor-is-valid)
- TuxedoVideoHero: replace animate-bounce with ease-out-expo
  (no-inline-bounce-easing)
- ProductTableClient: useCallback for handleDeleted
  (jsx-no-new-function-as-prop)
- excel-parser: pre-compile delimiter regexes (js-hoist-regexp)
- water-log/settings: Promise.all for parallel DB calls
  (async-parallel)
- ToastNotification: extract toast store to separate file
  (only-export-components)
- WholesaleClient: inline <WholesaleIcon/> instead of hoisting to
  const (rendering-hoist-jsx)

src/components/admin/SettingsClient.tsx

@@ -135,16 +135,14 @@ export default function SettingsClient({
   paymentSettings,
   currentUser,
 }: Props) {
-  const [activeTab, setActiveTab] = useState<Tab>("general");
-
-  // Handle URL hash for sidebar navigation
-  useEffect(() => {
+  // Initial tab is determined by URL hash if present, otherwise "general".
+  // No useEffect needed — we read window.location.hash during the lazy
+  // initializer on the client. On the server we default to "general".
+  const [activeTab, setActiveTab] = useState<Tab>(() => {
+    if (typeof window === "undefined") return "general";
     const hash = window.location.hash.slice(1);
-    const matchingTab = TABS.find(t => t.hash === hash);
-    if (matchingTab) {
-      setActiveTab(matchingTab.id);
-    }
-  }, []);
+    return TABS.find((t) => t.hash === hash)?.id ?? "general";
+  });
 
   return (
     <main className="min-h-screen bg-[var(--admin-bg)]">