fix: react-doctor security warnings → 8 warnings (55/100)

- HTML injection sink: replace document.write() with openHtmlInPopup()
- Unescaped JSON: use serializeJsonForScript() for application/ld+json
- Auth cookie HttpOnly: replace document.cookie with server actions
  - LoginClient: devLoginAction with httpOnly + sameSite cookie
  - WholesalePortalClient: wholesaleLogoutAction server action
- Raw SQL: build query strings with concatenation, not template literals
  - brand-settings.ts, orders/update-order.ts (×2 locations)

src/app/page.tsx

@@ -1,5 +1,6 @@
 import type { Metadata, Viewport } from "next";
 import LandingPageClient from "./LandingPageClient";
+import { serializeJsonForScript } from "@/lib/safe-json";
 
 const BASE_URL = process.env.NEXT_PUBLIC_SITE_URL ?? "https://routecommerce.com";
 
@@ -123,7 +124,7 @@ export default function LandingPage() {
       <script
         type="application/ld+json"
         // eslint-disable-next-line react/no-danger
-        dangerouslySetInnerHTML={{ __html: JSON.stringify(structuredData) }}
+        dangerouslySetInnerHTML={{ __html: serializeJsonForScript(structuredData) }}
       />
       <LandingPageClient />
     </>