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/ServicePolicy.php

@@ -89,6 +89,16 @@ class ServicePolicy
         return $teamId !== null && $user->isAdminOfTeam($teamId);
     }
 
+    /**
+     * Determine whether the user can upload a backup archive for a database within this service.
+     */
+    public function uploadBackup(User $user, Service $service): bool
+    {
+        $teamId = $this->getTeamId($service);
+
+        return $teamId !== null && $user->isAdminOfTeam($teamId);
+    }
+
     /**
      * Determine whether the user can deploy the service.
      */