feat(website): add the Stalker portal setup guide with mock-backed screenshots

Publish "How to Connect a Stalker or Ministra Portal to IPTVnator": the
portal URL shapes discovery accepts, MAC normalization, the optional
serial/device-ID/signature fields and the pinning rules behind the
"generate device IDs" toggle, what endpoint discovery does on Add, the
sections a portal source gets, Account info, and a troubleshooting list
built from the app's own refusal messages, plus a seven-question FAQ.
The guide is cross-linked from the download pages and llms.txt.

Guide screenshots come from the capture script. Shots that walk into a
Stalker portal start the stalker-mock-server and seed its marketing-demo
portal for that run only, so release shots never gain a third source
card. The frame guard allowlists exactly that scenario's MAC and keeps
rejecting every other MAC-shaped string.

To keep the live-TV frame free of third-party images, the fictional live
channel list and the channel-logo SVG renderer move into
@iptvnator/shared/marketing-fixtures; both mocks now serve
/assets/marketing/logo/<slug>.svg, the Stalker marketing-demo scenario
builds its ITV categories, channels and schedule from those fixtures
instead of faker names with picsum logos, and the mock resolves asset
URLs on get_all_channels too, which is the response the app renders
the channel list from.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

apps/website/src/components/blog/PostButton.astro

@@ -15,7 +15,11 @@ const { href, label, external = true } = Astro.props;
   class="not-prose group my-6 inline-flex items-center gap-2 rounded-lg border border-dashed border-accent-500/35 bg-accent-500/[0.08] px-4 py-2.5 text-sm font-medium text-accent-200 transition-all duration-200 hover:border-accent-400/50 hover:bg-accent-500/[0.14] hover:text-accent-100"
 >
   <span>{label ?? 'Open link'}</span>
-  <svg class="h-4 w-4 transition-transform duration-200 group-hover:translate-x-0.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="1.8">
-    <path stroke-linecap="round" stroke-linejoin="round" d="M13.5 4.5H19.5m0 0v6m0-6L10.5 13.5M6 6h3.75M6 10.5V18a1.5 1.5 0 001.5 1.5H15" />
+  <svg class="h-4 w-4 transition-transform duration-200 group-hover:translate-x-0.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="1.8" aria-hidden="true">
+    {external ? (
+      <path stroke-linecap="round" stroke-linejoin="round" d="M13.5 4.5H19.5m0 0v6m0-6L10.5 13.5M6 6h3.75M6 10.5V18a1.5 1.5 0 001.5 1.5H15" />
+    ) : (
+      <path stroke-linecap="round" stroke-linejoin="round" d="M17 8l4 4m0 0l-4 4m4-4H3" />
+    )}
   </svg>
 </a>