refactor: harmonize redirects after submitting forms

app/Views/Components/DropdownMenu.php

app/Views/Components/Forms/MarkdownEditor.php

app/Views/Components/Forms/MultiSelect.php

app/Views/Components/Forms/Select.php

app/Views/Components/Forms/Textarea.php

app/Views/errors/html/error_404.php

modules/Admin/Controllers/ContributorController.php

modules/Admin/Controllers/EpisodeController.php

modules/Admin/Controllers/PageController.php

modules/Admin/Controllers/PersonController.php

modules/Admin/Controllers/PodcastController.php

modules/Admin/Controllers/SoundbiteController.php

modules/Admin/Language/en/Contributor.php

modules/Admin/Language/en/Episode.php

modules/Admin/Language/en/Fediverse.php

modules/Admin/Language/en/Page.php

modules/Admin/Language/en/Person.php

modules/Admin/Language/en/Podcast.php

modules/Admin/Language/en/Soundbite.php

modules/Admin/Language/en/VideoClip.php