ads + i18n: forum/newsletter banners; smarter language autodetect

Forum:
  - /forum landing: switch to 2-col layout, add SidebarAdStack
    (300x600 + every 300x250) on the right.
  - /forum/thread/[id]: insert one 300x250 "Sponsored" tile after
    every 4 replies (idx 3, 7, 11 …). Trailing-ad guard so the last
    reply isn't followed by an ad with no replies after it. Cycles
    through the full ADS_300X250 pool by index so every banner gets
    impressions across long threads.

Newsletter:
  - /newsletter/archive: drop SidebarAdStack into the existing
    right rail above the signup CTA + topic browser.

LanguageSwitcher autodetect (US default for US users was failing):
  1. Timezone override: if the user is in America/*, Pacific/Honolulu,
     Pacific/Auckland|Wellington, Australia/*, Europe/London|Dublin,
     or Atlantic/Reykjavik — always return 'en'. Fixes US-based
     users whose OS locale happened to be set to a non-English value.
  2. Otherwise walk navigator.languages (the full preference list,
     not just navigator.language[0]) and pick the first base code we
     support (en/es/pt/fr/de/zh/ja/ar/hi).
  3. Fallback to 'en'.

  All non-en selections still route through Google Translate's hosted
  proxy on the .translate.goog subdomain — search engines and US
  visitors continue to only ever see English on broadcastbeat.com.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/forum/page.tsx

@@ -4,6 +4,7 @@ import Link from 'next/link';
 import Header from '@/components/Header';
 import Footer from '@/components/Footer';
 import AdImage from '@/components/AdImage';
+import SidebarAdStack from '@/components/SidebarAdStack';
 import { ADS_728X90, shuffle } from '@/lib/ads';
 import { createClient } from '@/lib/supabase/client';
 
@@ -274,6 +275,8 @@ export default function ForumIndexPage() {
         </div>
 
         <div className="max-w-container mx-auto px-4 py-6">
+          <div className="lg:grid lg:grid-cols-[1fr,300px] lg:gap-8">
+          <div>
 
           {/* Feed Mode Tabs */}
           <div className="flex items-center gap-1 bg-[#1a1a1a] border border-[#2a2a2a] rounded-lg p-1 mb-6 w-fit">
@@ -576,6 +579,15 @@ export default function ForumIndexPage() {
               <AdImage ad={shuffle(ADS_728X90)[0]} page="forum" />
             </div>
           )}
+
+          </div>
+          {/* Sidebar: 300x600 + every rotating 300x250 */}
+          <aside className="mt-10 lg:mt-0" aria-label="Advertisements">
+            <div className="lg:sticky lg:top-24">
+              <SidebarAdStack />
+            </div>
+          </aside>
+          </div>
         </div>
       </main>
       <Footer />