feat: add switch stack port config with dynamic serial resolution

- Add data source meraki_switch_stacks to resolve member serials by stack name
- Add switch_stack_port_configs variable: specify stack_name + port_range
  instead of individual switch serials
- Terraform applies port_range to ALL members of the stack automatically
- Merge switch_port_configs and switch_stack_port_configs into all_ports local
- Add example for bcn01-lab-stack01 (2x48p) in switch.auto.tfvars

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sites/BCN01-LAB/variables.tf

@@ -110,3 +110,18 @@ variable "switch_port_configs" {
   default     = []
   description = "Puertos de switch a configurar con 802.1X. Requiere serial del switch."
 }
+
+# Configuración de puertos por nombre de stack
+variable "switch_stack_port_configs" {
+  type = list(object({
+    stack_name           = string
+    port_range           = string
+    name                 = optional(string, "")
+    type                 = optional(string, "access")
+    vlan                 = optional(number, null)
+    access_policy_type   = optional(string, "Open")
+    access_policy_number = optional(number, null)
+  }))
+  default     = []
+  description = "Puertos de stack a configurar por nombre. Terraform resuelve los seriales automáticamente."
+}