refactor(policies): add uploadBackup ability and enforce it on backup upload endpoint

Introduce a dedicated `uploadBackup` ability on Application, Database,
Service, and ServiceDatabase policies (admin/owner only) and call
`$this->authorize('uploadBackup', $resource)` in `UploadController::upload`
so the backup-upload endpoint goes through the same policy layer as the
rest of the authorization refactor. Adds Pest coverage for each policy
variant plus HTTP-level checks.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/Policies/ServiceDatabasePolicy.php

@@ -63,4 +63,12 @@ class ServiceDatabasePolicy
     {
         return Gate::allows('update', $serviceDatabase->service);
     }
+
+    /**
+     * Determine whether the user can upload a backup archive for this service database.
+     */
+    public function uploadBackup(User $user, ServiceDatabase $serviceDatabase): bool
+    {
+        return Gate::allows('uploadBackup', $serviceDatabase->service);
+    }
 }