feat: lit/tb-assign – conditions with dry run on live templates, reattach

- ThemeBuilderAccess::changeableTemplate(): rights (Q18 not_found), group gate,
  no TB draft, never the default template, current template_rev
- omitted exclude_from stays, [] clears (Q3); live dry run shows use_on and
  exclude_from before/after, overlaps and possible overlaps (B9)
- reattach only with published layouts (B10) and a live TB post; always
  disabled, unmarks template and layouts; failure restores everything

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/ThemeBuilder/ThemeBuilderIntegration.php

@@ -52,6 +52,7 @@ final class ThemeBuilderIntegration implements Integration
         return [
             new TbListAbility($this->access, $conditions),
             new TbCreateTemplateAbility($this->access, $conditions, $this->composition, $this->saver, $this->log),
+            new TbAssignAbility($this->access, $conditions, $this->log),
         ];
     }
 }