perf: Self-host mermaid and load it only on pages with diagrams

Every page used to import mermaid (~2 MB of js) from cdn.jsdelivr.net
whether it contained a diagram or not. The mermaid-script partial now
checks for a .mermaid element and only then imports a self-hosted es
module build; mermaid's internal chunks lazy-load per diagram type.

The extension skips injecting its own script when the UI ships
partials/mermaid-script.hbs, so the mermaid_library_url/script_stem
playbook configuration is gone and no third-party CDN is involved.

Author: lfrancke

antora-playbook.yml

@@ -28,8 +28,6 @@ urls:
 antora:
   extensions:
     - require: '@sntke/antora-mermaid-extension'
-      mermaid_library_url: https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs
-      script_stem: mermaid-scripts
     - ./lib/stackable-operator-helpers.js
     - ./lib/llms-txt.js
 content:

local-antora-playbook.yml

@@ -13,8 +13,6 @@ urls:
 antora:
   extensions:
     - require: '@sntke/antora-mermaid-extension'
-      mermaid_library_url: https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs
-      script_stem: mermaid-scripts
     - ./lib/stackable-operator-helpers.js
     - ./lib/llms-txt.js
 content:

only-dev-antora-playbook.yml

@@ -13,8 +13,6 @@ urls:
 antora:
   extensions:
     - require: '@sntke/antora-mermaid-extension'
-      mermaid_library_url: https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs
-      script_stem: mermaid-scripts
     - ./lib/stackable-operator-helpers.js
     - ./lib/llms-txt.js
 content: