fix: move viewer to content folder

development/issues/closed/217.html

development/issues/closed/217.mjs

development/issues/open/289.html

development/issues/open/289.mjs

development/mock/issue-217.js

development/templates/vite.config.mjs

source/components/accessibility/locale-picker.mjs

source/components/content/style/viewer.pcss

source/components/content/stylesheet/viewer.mjs

source/components/content/viewer.mjs

source/components/datatable/change-button.mjs

source/components/datatable/dataset.mjs

source/components/datatable/datasource.mjs

source/components/datatable/datasource/rest.mjs

source/components/datatable/datatable.mjs

source/components/datatable/filter.mjs

source/components/datatable/save-button.mjs

source/components/datatable/status.mjs

source/components/form/action-button.mjs

source/components/form/button.mjs