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/phrasebook/backend/lang/en/lang.yaml

@@ -146,6 +146,7 @@ money:
   currency: "Currency: :code"
 taglist:
   invalid: "The :field field must be a list of tags."
+  not_allowed: "The tag :tag is not allowed."
   add: "Add a tag"
   remove: "Remove :tag"
 secret:

modules/phrasebook/backend/lang/pl/lang.yaml

@@ -156,6 +156,7 @@ money:
   currency: "Waluta: :code"
 taglist:
   invalid: "Pole :field musi być listą tagów."
+  not_allowed: "Tag :tag jest niedozwolony."
   add: "Dodaj tag"
   remove: "Usuń :tag"
 secret: