Fix remaining security vulnerabilities

- H1: Add missing sanitize() to help center content rendering
- H2: Tighten CSP by removing unsafe-inline/unsafe-eval from script-src;
  move theme init to external JS file with meta tag for defaultDark
- M1: Add SSRF protection for radio API URLs (block private IPs)
- M2: Add rate limiting to SSO ticket endpoint (5 req/30s per user)
- M4: Document locale validation safety in i18n dynamic import
- L1: Truncate stacktraces in admin commandocentrum to first 20 lines

src/app/admin/commandocentrum/page.tsx

@@ -423,8 +423,13 @@ export default async function CommandoCentrum() {
                 </tr>
               </thead>
               <tbody>
-                {errors.map((e) => {
+                  {errors.map((e) => {
                   const trace = decodeStacktrace(e.stacktrace);
+                  // Truncate stacktraces to first 20 lines to avoid info disclosure.
+                  const snippet = trace
+                    ? trace.split("\n").slice(0, 20).join("\n") +
+                      (trace.split("\n").length > 20 ? "\n… (truncated)" : "")
+                    : "(empty)";
                   return (
                     <tr key={e.id}>
                       <td className="text-sm text-gray-500 dark:text-gray-400 whitespace-nowrap">
@@ -436,7 +441,7 @@ export default async function CommandoCentrum() {
                       </td>
                       <td>
                         <pre className="text-xs p-2 bg-gray-50 dark:bg-black/20 rounded overflow-auto max-h-[160px]">
-                          {trace || "(empty)"}
+                          {snippet}
                         </pre>
                       </td>
                     </tr>

src/app/api/client/sso/route.ts

@@ -1,6 +1,7 @@
 import { headers } from "next/headers";
 import { auth } from "@/lib/auth";
 import { prisma } from "@/lib/prisma";
+import { clientIp, rateLimit } from "@/lib/rate-limit";
 import { siteSettings } from "@/lib/services/site-settings";
 import { issueSsoTicket } from "@/lib/auth/sso-ticket";
 
@@ -13,14 +14,18 @@ export async function GET() {
   }
 
   const userId = Number(session.user.id);
+
+  // Throttle SSO ticket generation (5 per 30s per user) — prevent ticket spam.
+  if (!rateLimit(`sso:${userId}`, 5, 30_000).ok) {
+    return new Response(JSON.stringify({ error: "Rate limited" }), { status: 429 });
+  }
+
   const [hotelName, clientUrl] = await Promise.all([
     siteSettings.get("hotel_name", "Atom"),
     siteSettings.get("nitro_client_url", ""),
   ]);
 
-  const hdrs = await headers();
-  const ip =
-    hdrs.get("x-forwarded-for")?.split(",")[0]?.trim() ?? hdrs.get("x-real-ip") ?? "0.0.0.0";
+  const ip = await clientIp();
 
   const ticket = await issueSsoTicket(prisma, userId, hotelName ?? "Atom", ip);
 

src/app/help/[category]/page.tsx

@@ -3,6 +3,7 @@ import Link from "next/link";
 import { notFound } from "next/navigation";
 import { ContentCard } from "@/components/public/ui";
 import { prisma } from "@/lib/prisma";
+import { sanitize } from "@/lib/sanitize";
 import { siteSettings } from "@/lib/services/site-settings";
 
 export const dynamic = "force-dynamic";
@@ -116,11 +117,10 @@ export default async function HelpCategoryPage({
           />
         ) : null}
 
-        {/* content is author-supplied HTML in AtomCMS (rendered raw with {!! !!}). */}
+        {/* content is author-supplied HTML — sanitised server-side. */}
         <div
           style={{ lineHeight: 1.7 }}
-          // biome-ignore lint/security/noDangerouslySetInnerHtml: author-supplied help content, matches AtomCMS Blade
-          dangerouslySetInnerHTML={{ __html: content }}
+          dangerouslySetInnerHTML={{ __html: sanitize(content) }}
         />
 
         {hasButton ? (

src/app/layout.tsx

@@ -51,12 +51,8 @@ export default async function RootLayout({ children }: { children: ReactNode })
   return (
     <html lang={locale} className={`app ${nunito.variable} ${pixelFont.variable}`}>
       <head>
-        {/* Apply the saved/default theme before first paint to avoid a flash. */}
-        <script
-          dangerouslySetInnerHTML={{
-            __html: `try{var s=localStorage.getItem('theme');if(s==='dark'||(!s&&${defaultDark}))document.documentElement.classList.add('dark');var nc=localStorage.getItem('navbarColor'),nt=localStorage.getItem('navbarTextColor');if(nc)document.documentElement.style.setProperty('--color-navbar',nc);if(nt)document.documentElement.style.setProperty('--color-navbar-text',nt);}catch(e){}`,
-          }}
-        />
+        <meta name="theme-default-dark" content={String(defaultDark)} />
+        <script src="/scripts/theme-init.js" />
       </head>
       <body
         className="flex min-h-screen flex-col site-bg"