Keep old pages readable, detect stale settings writes, make backups honest

- Own CSS is parsed on write only. A page whose stored CSS no longer
  passes a stricter rule answers 200 and opens in the editor; that one
  block loses its CSS. A document read several times in one request is
  validated once.
- Settings and theme refuse a write from an outdated form.
- A backup fails when a media file does not arrive completely and
  leaves no half directory behind; rotation counts intact backups only.
- The archive update takes its backup behind the maintenance page.
- A package import puts all media in place before removing the old
  ones, reports honestly when that fails and keeps a maintenance state
  that was already on.
- Restoring replaces the SQLite file in one move and points at pending
  migrations.
- Six irreversible actions ask first, in a dialog of the admin's own.
- Ctrl+S in the editor takes the field being typed in along; Delete
  no longer removes a block while a dialog is open.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

public/assets/form-editor.js

@@ -316,7 +316,12 @@ if (root) {
       if (toggle) { const card = toggle.closest('[data-field]'); setOpen(card, !card.classList.contains('is-open')); refresh(); return; }
       const button = event.target.closest('[data-remove-field]');
       if (!button) return;
-      button.closest('[data-field]').remove(); refresh(); add.focus();
+      const card = button.closest('[data-field]');
+      const name = card.querySelector('[data-field-label]')?.value.trim();
+      const remove = () => { card.remove(); refresh(); add.focus(); };
+      // Ein eben angelegtes, leeres Feld verschwindet ohne Frage; alles andere fragt nach.
+      if (!name || !window.kantConfirm) { remove(); return; }
+      window.kantConfirm({ title: `Feld „${name}“ entfernen?`, message: 'Bereits eingegangene Anfragen behalten ihre Angaben. Wirksam wird es erst mit „Speichern“.', confirmLabel: 'Feld entfernen', variant: 'danger', onConfirm: remove });
     });
     list.addEventListener('input', event => {
       const card = event.target.closest('[data-field]');