fix(pos): cargar empleados reales en login en vez de datos demo

- Nuevo endpoint GET /pos/api/auth/employees/<tenant_id>
- Login carga empleados dinamicamente del tenant
- Si hay 1 solo empleado, se auto-selecciona
- Removidos 6 usuarios hardcodeados del design system

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/blueprints/auth_bp.py

@@ -157,6 +157,38 @@ def login_pin():
     })
 
 
+@auth_bp.route('/employees/<int:tenant_id>', methods=['GET'])
+def list_login_employees(tenant_id):
+    """Public endpoint: list employees for the login screen (names + roles only, no sensitive data)."""
+    try:
+        conn = get_tenant_conn(tenant_id)
+    except ValueError:
+        return jsonify({'error': 'Tenant not found'}), 404
+
+    cur = conn.cursor()
+    cur.execute("""
+        SELECT id, name, role FROM employees
+        WHERE is_active = true AND pin IS NOT NULL
+        ORDER BY name
+    """)
+    employees = []
+    for row in cur.fetchall():
+        name = row[1]
+        parts = name.split()
+        initials = ''.join([p[0].upper() for p in parts[:2]]) if parts else '?'
+        role_labels = {'owner': 'Dueño', 'admin': 'Administrador', 'cashier': 'Cajero', 'warehouse': 'Almacén', 'accountant': 'Contador'}
+        employees.append({
+            'id': row[0],
+            'name': name,
+            'initials': initials,
+            'role': row[2],
+            'role_label': role_labels.get(row[2], row[2])
+        })
+    cur.close()
+    conn.close()
+    return jsonify({'data': employees})
+
+
 @auth_bp.route('/me', methods=['GET'])
 def auth_me():
     """Get current employee info from token."""