Touched entity timestamps on entity tag update

Decided it's relevant to entity updated_at since tags are now indexed
alongside content.

- Also fixed tags not applied on shelf.
- Also enforced proper page API update validation.
- Adds tests to cover.

For #3319
Fixes #3370

app/Http/Controllers/Api/BookshelfApiController.php

@@ -11,21 +11,20 @@ use Illuminate\Validation\ValidationException;
 
 class BookshelfApiController extends ApiController
 {
-    /**
-     * @var BookshelfRepo
-     */
-    protected $bookshelfRepo;
+    protected BookshelfRepo $bookshelfRepo;
 
     protected $rules = [
         'create' => [
             'name'        => ['required', 'string', 'max:255'],
             'description' => ['string', 'max:1000'],
             'books'       => ['array'],
+            'tags'        => ['array'],
         ],
         'update' => [
             'name'        => ['string', 'min:1', 'max:255'],
             'description' => ['string', 'max:1000'],
             'books'       => ['array'],
+            'tags'        => ['array'],
         ],
     ];