feat: add supported sites page, remove yt-dlp mentions from public copy

yt-dlp is an internal implementation detail and should not be exposed
on the public site. Replace direct mentions in the platforms and FAQ
sections with a link to a new /supported-sites page listing every
extractor from yt-dlp's supported-sites doc (searchable, grouped
alphabetically), translated across en/fr/es/it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/SupportedPlatformsSection.tsx

@@ -1,4 +1,5 @@
 import { getTranslations } from 'next-intl/server'
+import { Link } from '@/navigation'
 
 const PLATFORMS = [
   'YouTube',
@@ -33,7 +34,15 @@ export async function SupportedPlatformsSection({ locale }: { locale: string })
             </span>
           ))}
         </div>
-        <p className="mt-4 text-sm text-gray-400 dark:text-slate-500">{t('more')}</p>
+        <p className="mt-4 text-sm text-gray-400 dark:text-slate-500">
+          {t.rich('more', {
+            link: (chunks) => (
+              <Link href="/supported-sites" className="text-violet-600 dark:text-violet-400 hover:underline">
+                {chunks}
+              </Link>
+            ),
+          })}
+        </p>
         <p className="mt-6 text-xs text-gray-400 dark:text-slate-500 max-w-2xl mx-auto">{t('disclaimer')}</p>
       </div>
     </section>