fix(seeder): prevent duplicate user on db:seed

[Icegreeen]

The DatabaseSeeder used User::factory()->create() and failed when running php artisan db:seed multiple times due to the unique email constraint.

It was updated to User::firstOrCreate() to ensure idempotency:

• No duplicate users are created.
• A predictable default user is always available ([email protected] / password).

Now it has no problems and does not break when running it multiple times.

[joetannenbaum]

Thanks!