refactor: move dateHelperVCalendar.js from common to frontend

That nobody has the idea to reuse it in pdf or print.
We only need to calculate a timestamp representing the DateTime
received in UTC as the same DateTime in the local timezone.

frontend/src/components/program/picasso/Picasso.vue

@@ -83,10 +83,7 @@ import { useDragAndDropNew } from './useDragAndDropNew.js'
 import { useDragAndDropReminder } from './useDragAndDropReminder.js'
 import { apiStore as api } from '@/plugins/store'
 import mergeListeners from '@/helpers/mergeListeners.js'
-import {
-  timestampToUtcString,
-  utcStringToTimestamp,
-} from '@/common/helpers/dateHelperVCalendar.js'
+import { timestampToUtcString, utcStringToTimestamp } from './dateHelperVCalendar.js'
 import DayResponsibles from './DayResponsibles.vue'
 import { ONE_DAY_IN_MILLISECONDS } from '@/helpers/vCalendarDragAndDrop.js'
 import { errorToMultiLineToast } from '@/components/toast/toasts'

frontend/src/components/program/picasso/PicassoEntry.vue

@@ -127,7 +127,7 @@
 import { ref, toRefs } from 'vue'
 import DialogActivityEdit from '../DialogActivityEdit.vue'
 import campCollaborationDisplayName from '@/common/helpers/campCollaborationDisplayName.js'
-import { timestampToUtcString } from '@/common/helpers/dateHelperVCalendar.js'
+import { timestampToUtcString } from './dateHelperVCalendar.js'
 import { dateHelperUTCFormatted } from '@/mixins/dateHelperUTCFormatted.js'
 import { scheduleEntryRoute } from '@/router.js'
 import router from '@/router.js'

common/helpers/dateHelperVCalendar.js → frontend/src/components/program/picasso/dateHelperVCalendar.js

@@ -1,4 +1,4 @@
-import dayjs from './dayjs.js'
+import dayjs from '@/common/helpers/dayjs.js'
 
 // converts a timestamp (local timezone) into ISO String format (UTC timezone)
 function timestampToUtcString(timestamp) {