fix: tb-assign reattaches only templates no Theme Builder post lists (audit L4)

"Detached" now means for lit/tb-assign what lit/tb-list shows as detached:
DiviThemeBuilder::isListedAnywhere() looks for any _et_template row (live,
draft or Theme Builder library post). A template another Theme Builder post
lists is refused with or without reattach; nothing is written.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

tests/Unit/Integrations/Divi/ThemeBuilder/TbAssignAbilityTest.php

@@ -180,6 +180,27 @@ final class TbAssignAbilityTest extends TestCase
         self::assertTrue($result['previous']['enabled']);
     }
 
+    /**
+     * Audit L4: reattach takes only templates no Theme Builder post lists (tb-list's detached) – not one that a
+     * Theme Builder library item or draft lists; nothing is written.
+     */
+    public function testReattachRefusesATemplateAnotherThemeBuilderPostLists(): void
+    {
+        $listedElsewhere = ThemeBuilderFixtures::template(1066, ['attached' => false]);
+        $store = ThemeBuilderFixtures::store([], 0, [], [$listedElsewhere]);
+        $store->allows('isListedAnywhere')->with(1066)->andReturn(true);
+        foreach (['setEnabled', 'attach', 'unmarkUnused', 'setConditions'] as $method) {
+            $store->shouldReceive($method)->never();
+        }
+
+        foreach ([['reattach' => true], []] as $extra) {
+            $refused = self::ability($store, FakeChangeLog::forbidden())->execute(self::input($listedElsewhere, $extra));
+            self::assertToolError($refused, 'validation_failed');
+            self::assertStringContainsString('keine entfernte Vorlage', self::clientError($refused)['message']);
+            self::assertArrayHasKey('template_id', self::errorFields($refused));
+        }
+    }
+
     /** Ruling Q8/B10: a layout Divi trashed meanwhile blocks the reattach; nothing is written. */
     public function testReattachNeedsPublishedLayouts(): void
     {