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- Settings and theme refuse a write from an outdated form.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>

tests/BacklogTest.php

@@ -12,6 +12,7 @@ use App\Content\PostRepository;
 use App\Content\SiteSettings;
 use App\Content\Theme;
 use App\Domain\InvalidDocument;
+use App\Domain\StaleWrite;
 use App\Infrastructure\ConnectionFactory;
 use App\Kernel;
 use App\Ops\ArchiveUpdate;
@@ -163,6 +164,65 @@ final class BacklogTest extends TestCase
         self::assertStringContainsString('Dieses Feld wird benötigt.', $antwort->getContent());
     }
 
+    public function testAPageWhoseStoredCssNoLongerPassesStaysReachableAndEditable(): void
+    {
+        // Gespeichert wurde, was beim Speichern galt. Ist eine Regel inzwischen strenger, fällt das
+        // CSS dieses einen Blocks weg (ADR 116) - die Seite antwortet nicht mit 500 und lässt sich
+        // zum Reparieren öffnen. Vorher warf schon das Lesen.
+        $document = DemoContent::starter('Altbestand');
+        $document['blocks'][] = ['id' => 'alt-text', 'type' => 'text', 'props' => ['text' => 'Bleibt lesbar'], 'css' => 'color: red;'];
+        $this->publishHome($document);
+        $alt = '& ~ p { color: red }';
+        try {
+            (new DocumentValidator())->validate([...$document, 'schemaVersion' => 23, 'blocks' => [...array_slice($document['blocks'], 0, -1), ['id' => 'alt-text', 'type' => 'text', 'props' => ['text' => 'Bleibt lesbar'], 'css' => $alt]]], writing: true);
+            self::fail('Dieses CSS muss beim Speichern abgelehnt werden, sonst prüft der Test nichts.');
+        } catch (InvalidDocument) {
+        }
+        foreach ($this->db->fetchAllAssociative('SELECT id, document FROM revision WHERE page_id = ?', ['page-1']) as $fassung) {
+            $this->db->update('revision', ['document' => str_replace('color: red;', $alt, $fassung['document'])], ['id' => $fassung['id']]);
+        }
+
+        $antwort = $this->request('/');
+        self::assertSame(200, $antwort->getStatusCode());
+        self::assertStringContainsString('Bleibt lesbar', $antwort->getContent());
+        self::assertStringNotContainsString('~ p', $antwort->getContent(), 'Das abgelehnte CSS wird nicht ausgegeben.');
+        $entwurf = $this->pages->findForEditor('page-1');
+        self::assertSame($alt, end($entwurf['document']['blocks'])['css'], 'Im Editor steht es noch da und lässt sich korrigieren.');
+
+        // Speichern verlangt weiter gültiges CSS.
+        $this->expectException(InvalidDocument::class);
+        $this->pages->saveDraft('page-1', $entwurf['document'], $entwurf['version']);
+    }
+
+    public function testSettingsAndThemeRefuseAWriteFromAnOutdatedForm(): void
+    {
+        // Zwei Admins haben dasselbe Formular offen. Der zweite überschrieb bisher still, was der
+        // erste gespeichert hatte. Jetzt trägt das Formular eine Kennung des geladenen Stands.
+        $werte = ['legalName' => 'Erste GmbH'];
+        $geladen = $this->site->stamp();
+        $this->site->save($werte, $geladen);
+        self::assertNotSame($geladen, $this->site->stamp());
+        try {
+            $this->site->save([...$werte, 'legalName' => 'Zweite GmbH'], $geladen);
+            self::fail('Der veraltete Stand muss abgelehnt werden.');
+        } catch (StaleWrite) {
+        }
+        self::assertSame('Erste GmbH', $this->site->load()['legalName']);
+        $this->site->save([...$werte, 'legalName' => 'Zweite GmbH'], $this->site->stamp());
+        self::assertSame('Zweite GmbH', $this->site->load()['legalName']);
+
+        $theme = new Theme($this->db);
+        $stand = $theme->load();
+        $geladen = $theme->stamp();
+        $theme->save($stand['colors'], $stand['fonts'], [...$stand['base'], 'linkUnderline' => null], null, $geladen);
+        try {
+            $theme->save($stand['colors'], $stand['fonts'], $stand['base'], null, $geladen);
+            self::fail('Der veraltete Stand muss abgelehnt werden.');
+        } catch (StaleWrite) {
+        }
+        self::assertFalse($theme->load()['base']['linkUnderline'], 'Die erste Änderung bleibt.');
+    }
+
     public function testAFormInTheFooterCanBeSentFromAnArchive(): void
     {
         (new FormRepository($this->db))->save('kontakt', 'Kontakt', [