Fix R15: gate demo seeder to local/testing

`migrate --seed` runs in the documented bootstrap; without a guard a production
deploy would get the mock household (stale/open/low-battery devices) in real
tables. DemoHomeSeeder now only runs in local/testing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

database/seeders/DatabaseSeeder.php

@@ -36,6 +36,10 @@ class DatabaseSeeder extends Seeder
             ],
         );
 
-        $this->call(DemoHomeSeeder::class);
+        // Demo household is development-only — never inject mock devices/warnings into
+        // a real (production) deployment via `migrate --seed`.
+        if (app()->environment('local', 'testing')) {
+            $this->call(DemoHomeSeeder::class);
+        }
     }
 }