feat(18.1-01): task 2 taglist string mode, customTags and all save sites

- string mode: split on the separator (comma or whitespace), normalised,
  stored joined by a comma or one space; null stores an empty string
- customTags false refuses a tag outside options (taglist.not_allowed)
- taglist checked and hydrated on relation forms and settings forms;
  settings bind taglist columns; required checked on the tags
- admin: TaglistField string mode and closed option lists, preview renders
  the tags read-only as a comma-separated list; rebuilt dist
- docs: Taglist section covers both modes, separator and customTags

modules/boardwalk/dist/index.html

@@ -7,7 +7,7 @@
     <meta name="summer-admin-base" content="__SUMMER_ADMIN_BASE__" />
     <link rel="icon" href="./favicon.ico" sizes="48x48" />
     <title>SummerCMS</title>
-    <script type="module" crossorigin src="./assets/index-DBhf-zrM.js"></script>
+    <script type="module" crossorigin src="./assets/index-CpHJmq2q.js"></script>
     <link rel="stylesheet" crossorigin href="./assets/index-CS4sv1WG.css">
   </head>
   <body>