docs: port still-relevant WHMCS KB articles to the dedicated KB

First step of retiring the WHMCS knowledgebase in favour of
kb.anhonesthost.com. Ports the four articles that are still accurate and
product-agnostic, into three new top-level sections:

- domains/  — transferring a domain, flushing a local DNS cache
- email/    — why we filter outbound mail
- support/  — remote support via RustDesk

Content was refreshed rather than copied verbatim:
- RustDesk download links were pinned to 1.3.8; now point at /releases/latest
  (current is 1.4.9). API server switched to https, which the relay serves.
- macOS DNS flush gained the killall mDNSResponder step, without which the
  documented command usually appears to do nothing.
- The nameserver list was deliberately not ported — this KB points customers
  at Dashboard → Server Information instead of hardcoding per-server values.
- Added an anti-social-engineering warning to the remote-support page.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

astro.config.mjs

@@ -19,6 +19,9 @@ export default defineConfig({
     '/whp/reference/': '/whp/reference/service-hostnames/',
     '/whp/add-ons/': '/whp/add-ons/overview/',
     '/whp/admin/': '/whp/admin/overview/',
+    '/domains/': '/domains/transferring-a-domain-to-us/',
+    '/email/': '/email/outbound-spam-filtering/',
+    '/support/': '/support/remote-support/',
   },
   vite: {
     resolve: {
@@ -85,6 +88,18 @@ export default defineConfig({
             },
           ],
         },
+        {
+          label: 'Domains',
+          items: [{ autogenerate: { directory: 'domains' } }],
+        },
+        {
+          label: 'Email',
+          items: [{ autogenerate: { directory: 'email' } }],
+        },
+        {
+          label: 'Support',
+          items: [{ autogenerate: { directory: 'support' } }],
+        },
         // Future products only appear once they have content.
       ],
       pagefind: true,