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- Settings and theme refuse a write from an outdated form.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/admin.css

@@ -1155,7 +1155,13 @@ details.form-card > summary.form-card-summary::before, details.form-card[open] >
 .update-lauf .secondary { background: transparent; color: #fff; border-color: #ffffff66 }
 .update-letztes { margin: 0 0 12px }
 .update-manual { margin-top: 6px }
-.update-dialog { max-width: 460px; border: 0; border-radius: 12px; padding: 24px 26px; box-shadow: 0 18px 48px #0003 }
-.update-dialog::backdrop { background: #1f2d2766 }
-.update-dialog h2 { margin: 0 0 10px; font-size: 18px }
-.update-dialog .dialog-actions { display: flex; justify-content: flex-end; gap: 10px; margin-top: 18px }
+.update-dialog, .confirm-dialog { max-width: 460px; border: 0; border-radius: 12px; padding: 24px 26px; box-shadow: 0 18px 48px #0003 }
+.update-dialog::backdrop, .confirm-dialog::backdrop { background: #1f2d2766 }
+.update-dialog h2, .confirm-dialog h2 { margin: 0 0 10px; font-size: 18px }
+.update-dialog .dialog-actions, .confirm-dialog .dialog-actions { display: flex; justify-content: flex-end; gap: 10px; margin-top: 18px }
+/* Die Rückfrage vor etwas Endgültigem (confirm.js). */
+.confirm-dialog { width: calc(100vw - 32px); color: var(--ink) }
+.confirm-dialog p { margin: 0; color: var(--muted); line-height: 1.5 }
+.confirm-dialog .dialog-actions .primary, .confirm-dialog .dialog-actions .secondary { margin: 0 }
+.primary.danger { background: var(--danger); border-color: var(--danger) }
+.primary.danger:hover:not(:disabled) { background: #6f251b; border-color: #6f251b }