feat: funciones Go para API Metabase y tipo MetabaseClient

Añade funciones Go stub para la API de Metabase en dominio infra:
auth, CRUD de cards, dashboards y users, execute_query y execute_card.
Incluye tipo MetabaseClient y helper HTTP compartido.
Todas las funciones son impuras con stubs not-implemented.

functions/infra/metabase_delete_dashboard.md

@@ -0,0 +1,37 @@
+---
+name: metabase_delete_dashboard
+kind: function
+lang: go
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "func MetabaseDeleteDashboard(client MetabaseClient, dashboardID int) error"
+description: "Elimina permanentemente un dashboard de Metabase. Accion irreversible. Para soft-delete usar MetabaseUpdateDashboard con archived:true. Endpoint: DELETE /api/dashboard/:id."
+tags: [metabase, dashboard, delete, api]
+uses_functions: []
+uses_types: [MetabaseClient_go_infra]
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [fmt]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "functions/infra/metabase_delete_dashboard.go"
+---
+
+## Ejemplo
+
+```go
+// Eliminar permanentemente
+err := MetabaseDeleteDashboard(client, 1)
+
+// Preferir soft-delete:
+// MetabaseUpdateDashboard(client, 1, map[string]any{"archived": true})
+```
+
+## Notas
+
+**ATENCION**: Esta operacion es irreversible. El dashboard y todas sus dashcards se eliminan permanentemente.
+
+Para un borrado seguro, preferir archivar con `MetabaseUpdateDashboard(client, dashboardID, map[string]any{"archived": true})`.