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_list_dashboards.md

@@ -0,0 +1,57 @@
+---
+name: metabase_list_dashboards
+kind: function
+lang: go
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "func MetabaseListDashboards(client MetabaseClient, filter string) ([]map[string]any, error)"
+description: "Lista dashboards de Metabase con filtro opcional. Retorna array de dashboards resumidos (sin dashcards). Endpoint: GET /api/dashboard."
+tags: [metabase, dashboard, list, 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_list_dashboards.go"
+---
+
+## Ejemplo
+
+```go
+// Listar todos los dashboards
+dashboards, err := MetabaseListDashboards(client, "all")
+
+// Solo mis dashboards
+dashboards, err := MetabaseListDashboards(client, "mine")
+
+// Dashboards archivados
+dashboards, err := MetabaseListDashboards(client, "archived")
+```
+
+## Notas
+
+### Parametros para un LLM
+
+| Parametro | Tipo | Requerido | Descripcion |
+|-----------|------|-----------|-------------|
+| client | MetabaseClient | si | Cliente autenticado |
+| filter | string | no | "all", "mine", "archived". Vacio = todas |
+
+Retorna dashboards resumidos (sin cards). Para ver las cards de un dashboard, usar MetabaseGetDashboard.
+
+### Campos principales de cada dashboard
+
+| Campo | Tipo | Descripcion |
+|-------|------|-------------|
+| id | float64 | ID del dashboard |
+| name | string | Nombre |
+| description | string | Descripcion |
+| collection_id | float64 | Coleccion contenedora |
+| creator_id | float64 | ID del creador |
+| archived | bool | Archivado |
+| created_at | string | Fecha creacion |