fixup: add ADRs for MyST migration decisions

Author: lundybernard

docs/decisions/0001-myst-migration/0002-shortcode-mapping.md

@@ -20,7 +20,6 @@ not one per file), using the following canonical mappings:
 
 ```
 {{< grid columns="1 2 2 3" >}}   →   ::::{grid} 1 2 2 3
-                                      :gutter: 2
 
 [[item]]                          →   :::{card} <title>
   type = 'card'                         :link: <link>

docs/decisions/0001-myst-migration/PLAN.md

@@ -161,7 +161,6 @@ mapping pattern **once per shortcode type**, not nine times.
 
      ```
      {{< grid columns="1 2 2 3" >}}     →   ::::{grid} 1 2 2 3
-                                            :gutter: 2
 
      [[item]]                            →   :::{card} <title>
      type = 'card'                            :link: <link>