feat: show full supported-platforms block on each downloader page

Replace the plain "looking for another platform?" text link at the
bottom of each per-platform page with the same SupportedPlatformsSection
used on the homepage, giving stronger internal linking between all
platform pages. Drop the now-unused otherPlatforms/browseAll strings.

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

messages/en.json

@@ -96,9 +96,7 @@
     "heading": "{platform} Downloader",
     "subheading": "Paste a {platform} link below and get your file in seconds — free, no account required.",
     "aboutHeading": "About downloading from {platform}",
-    "faqHeading": "{platform} downloader FAQ",
-    "otherPlatforms": "Looking for another platform?",
-    "browseAll": "Browse all supported sites"
+    "faqHeading": "{platform} downloader FAQ"
   },
   "downloaderPages": {
     "youtube": {