fix: Corregir autenticación API, bypass de pago y relaciones de modelos

- Corregir middleware Authenticate para retornar JSON 401 en rutas API
- Agregar método unauthenticated() en Handler para respuestas JSON
- Implementar bypass de pago en ContractController
- Corregir relaciones belongsToMany en Postulations y Suppliers
- Corregir concatenación de strings en NoHomeController

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Models/Suppliers.php

@@ -55,7 +55,7 @@ class Suppliers extends Model
 
     public function postulations()
     {
-        return $this->belongsToMany(Postulations::class)->withTimestamps();
+        return $this->belongsToMany(Postulations::class, 'postulations_suppliers', 'suppliers_id', 'postulations_id')->withTimestamps();
     }
 
     public function payments()