Add cac-litespeed image family (OpenLiteSpeed, native LSAPI)

New paid-tier per-customer image built on litespeedtech/openlitespeed:1.8.4-lsphpNN.
Matrix: 8.1-8.5. Native LSAPI suexec to customer uid, server-level LSCache,
all WP/WooCommerce extensions (memcached, redis, imagick, mbstring, etc.) baked in.

Files:
- Dockerfile.litespeed (FROM prebuilt LiteSpeed base, layers wp-cli/composer/mariadb)
- configs/litespeed/{httpd_config,site-template,lsphp-overrides}.tpl
- scripts/{entrypoint,create-vhost,detect-memory}-litespeed.sh + install-lscache-wp.sh

CI: new Build-LiteSpeed-Images matrix job. OLS_VERSION pinned to 1.8.4 (only
release with prebuilt images for all 5 PHP versions on Docker Hub).

Spec: whp/docs/superpowers/specs/2026-06-01-cac-litespeed-design.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

configs/litespeed/vhconf.tpl

@@ -0,0 +1,77 @@
+## Per-vhost config — rendered at container start.
+## Templated vars (envsubst allow-list): $user $domain
+## Anything that looks like $DOC_ROOT, $VH_ROOT, $HTTP_HOST etc. is an OLS
+## runtime macro — intentionally NOT in the envsubst allow-list so it
+## passes through unchanged for OLS to expand at request time.
+
+docRoot                   /home/${user}/public_html
+
+enableGzip                1
+enableBr                  1
+
+errorlog /home/${user}/logs/litespeed/error.log {
+  useServer               0
+  logLevel                WARN
+  rollingSize             10M
+  keepDays                14
+  compressArchive         1
+}
+
+accesslog /home/${user}/logs/litespeed/access.log {
+  useServer               0
+  rollingSize             10M
+  keepDays                7
+  compressArchive         1
+}
+
+index  {
+  useServer               0
+  indexFiles              index.php, index.html
+  autoIndex               0
+}
+
+scripthandler  {
+  add                     lsapi:lsphp php
+}
+
+## LSCache plugin owns Cache-Control / Expires entirely — keep server-level
+## expires off so we don't double-emit headers.
+expires  {
+  enableExpires           0
+}
+
+accessControl  {
+  allow                   *
+}
+
+context / {
+  ## $DOC_ROOT is an OLS macro (not a shell var). Don't add it to the
+  ## envsubst allow-list in create-vhost-litespeed.sh or it'll expand to
+  ## empty and break docroot resolution.
+  location                $DOC_ROOT/
+  allowBrowse             1
+  rewrite  {
+    enable                1
+    inherit               0
+    autoLoadHtaccess      1
+    RewriteFile           .htaccess
+  }
+  addDefaultCharset       off
+}
+
+rewrite  {
+  enable                  1
+  autoLoadHtaccess        1
+  logLevel                0
+}
+
+## Per-vhost LSCache storage. Server module cache{} block enables the engine;
+## these lines tell the vhost WHERE to cache. The LSCWP plugin flips the
+## cache on/off at request time via X-LiteSpeed-Cache-Control headers.
+module cache {
+  storagePath             /home/${user}/lscache
+  checkPrivateCache       1
+  checkPublicCache        1
+  enableCache             0
+  enablePrivateCache      0
+}