Fix Scramble API docs warnings

Remove redundant @var annotations from API resources and defer the user
access in the email unique rule of UserUpdateRequest, so rules() can be
evaluated by Scramble without route model binding. Add a test that fails
on any Scramble diagnostic and tests for the email unique rule.

app/Http/Resources/V1/ProjectMember/ProjectMemberResource.php

@@ -21,13 +21,13 @@ class ProjectMemberResource extends BaseResource
     public function toArray(Request $request): array
     {
         return [
-            /** @var string $id ID of project member */
+            /** ID of project member */
             'id' => $this->resource->id,
-            /** @var int|null $billable_rate Billable rate in cents per hour */
+            /** Billable rate in cents per hour */
             'billable_rate' => $this->resource->billable_rate,
-            /** @var string $member_id ID of the organization member */
+            /** ID of the organization member */
             'member_id' => $this->resource->member_id,
-            /** @var string $project_id ID of the project */
+            /** ID of the project */
             'project_id' => $this->resource->project_id,
         ];
     }