Remove unused model constants

- Company: COMPANY_LEVEL, CUSTOMER_LEVEL (never referenced)
- Payment: all 5 PAYMENT_MODE_* constants (never referenced)
- Transaction: PENDING (never referenced)

RecurringInvoice constants (ACTIVE, ON_HOLD, NONE, COUNT, DATE) are kept
as they are used via hardcoded strings in services, factories, and migrations.

app/Models/Company.php

@@ -21,10 +21,6 @@ class Company extends Model implements HasMedia
         'id',
     ];
 
-    public const COMPANY_LEVEL = 'company_level';
-
-    public const CUSTOMER_LEVEL = 'customer_level';
-
     protected $appends = ['logo', 'logo_path'];
 
     public function getRolesAttribute()