docs(local-dev): add 'Local development' section + PHP 8.5 support

Adds /whp/local-dev/ with three articles documenting the public cloud
container images on repo.anhonesthost.net/cloud-hosting-platform/:

- overview: dev/prod parity pitch, prerequisites, table of images,
  link to the Gitea org, and a note that this is for customers
  comfortable with Docker (the hosted side needs none of this).
- php-apache: cloud-apache-container (cac). PHP 7.4 through 8.5 side
  by side, default 8.3, AlmaLinux 9 + Apache mod_ssl. Documents
  image tags, local-dev.sh flags, manual docker command, bind-mount
  layout, WordPress install, helper scripts (instance_start /
  instance_stop / instance_logs / instance_db_info), and cleanup.
- node: cloud-node-container (cnoc). Node 18/20/22, default 20,
  AlmaLinux 9 + Nginx (SSL + HTTP→HTTPS redirect) + PM2 +
  Memcached. Same shape: tags, flags, manual docker, where code
  goes (user/app/), logs layout, helpers, cleanup.

Sidebar gains a 'Local development' group between Site Builder and
Reference. Section redirect /whp/local-dev/ -> overview added to
the section-landing redirect set.

astro.config.mjs

@@ -15,6 +15,7 @@ export default defineConfig({
     '/whp/getting-started/': '/whp/getting-started/welcome/',
     '/whp/how-to/': '/whp/how-to/add-a-domain/',
     '/whp/site-builder/': '/whp/site-builder/overview/',
+    '/whp/local-dev/': '/whp/local-dev/overview/',
     '/whp/reference/': '/whp/reference/service-hostnames/',
     '/whp/add-ons/': '/whp/add-ons/overview/',
     '/whp/admin/': '/whp/admin/overview/',
@@ -65,6 +66,10 @@ export default defineConfig({
               badge: { text: 'Beta', variant: 'tip' },
               items: [{ autogenerate: { directory: 'whp/site-builder' } }],
             },
+            {
+              label: 'Local development',
+              items: [{ autogenerate: { directory: 'whp/local-dev' } }],
+            },
             {
               label: 'Reference',
               items: [{ autogenerate: { directory: 'whp/reference' } }],