feat(metabase): nuevos modulos — snippets, notifications, dashboard_filters

Tres modulos nuevos con funciones CRUD completas:
- snippets: list, get, create, update, archive (SQL reutilizable)
- notifications: list, create_card_alert, create_dashboard_subscription, update, delete
- dashboard_filters: add_dashboard_filter (parameter_mappings sobre cards existentes)

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

python/functions/metabase/metabase_get_snippet.md

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+---
+name: metabase_get_snippet
+kind: function
+lang: py
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "def metabase_get_snippet(client: MetabaseClient, snippet_id: int) -> dict"
+description: "Obtiene un SQL snippet de Metabase por su ID. Endpoint: GET /api/native-query-snippet/:id."
+tags: [metabase, snippet, get, api, python]
+uses_functions: []
+uses_types: [MetabaseClient_go_infra]
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [httpx]
+params:
+  - name: client
+    desc: "instancia autenticada de MetabaseClient"
+  - name: snippet_id
+    desc: "ID numerico del snippet a obtener"
+output: "dict: snippet completo con id, name, content, description, collection_id, creator_id, archived, created_at, updated_at"
+tested: false
+tests: []
+test_file_path: ""
+file_path: "python/functions/metabase/snippets.py"
+---
+
+## Ejemplo
+
+```python
+snippet = metabase_get_snippet(client, 42)
+print(snippet["name"])
+print(snippet["content"])
+print(snippet["description"])
+```
+
+## Notas
+
+Retorna 404 si el snippet no existe.
+Util para verificar el contenido actual antes de hacer un update.