feat(metabase): expansion cards y documents — export, model, ProseMirror validation, copy nativo

Cards: export_card (CSV/XLSX/JSON), create_model (type=model para fuentes MBQL).
Documents: prosemirror_card_embed helper (resizeNode envolviendo cardEmbed),
validacion automatica contra whitelist TipTap antes de enviar, copy_document
refactorizado al endpoint nativo POST /api/document/:id/copy.
Docs: dataset_query legacy vs MBQL5, template-tags, whitelist de nodos.

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

python/functions/metabase/prosemirror_card_embed.md

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+---
+name: prosemirror_card_embed
+kind: function
+lang: py
+domain: infra
+version: "1.0.0"
+purity: pure
+signature: "def prosemirror_card_embed(card_id: int, height: int = 400) -> dict"
+description: "Genera un nodo ProseMirror cardEmbed envuelto en resizeNode con altura adecuada. Un cardEmbed desnudo renderiza con ~50px — este helper produce el formato que Metabase espera para que la card se vea bien."
+tags: [metabase, document, prosemirror, cardEmbed, resizeNode, pure, python]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: [uuid]
+params:
+  - name: card_id
+    desc: "ID de la card/pregunta de Metabase a embeber"
+  - name: height
+    desc: "altura en pixeles del embed (default 400). minHeight se fija en 280"
+output: "dict ProseMirror: nodo resizeNode > cardEmbed, insertable en el array content de un document"
+tested: false
+tests: []
+test_file_path: ""
+file_path: "python/functions/metabase/documents.py"
+---
+
+## Ejemplo
+
+```python
+from metabase.documents import metabase_create_document, prosemirror_card_embed
+
+doc = metabase_create_document(client, "Reporte", {
+    "type": "doc",
+    "content": [
+        {"type": "heading", "attrs": {"level": 2},
+         "content": [{"type": "text", "text": "Revenue"}]},
+        prosemirror_card_embed(7711, height=500),
+        {"type": "paragraph",
+         "content": [{"type": "text", "text": "Datos actualizados."}]},
+    ]
+})
+```
+
+## Por qué existe este helper
+
+```python
+# MAL — cardEmbed desnudo: renderiza con ~50px de alto, ilegible
+{"type": "cardEmbed", "attrs": {"id": 42}}
+
+# BIEN — prosemirror_card_embed: envuelto en resizeNode
+prosemirror_card_embed(42, height=450)
+# → {"type": "resizeNode", "attrs": {"height": 450, "minHeight": 280},
+#    "content": [{"type": "cardEmbed", "attrs": {"id": 42, "_id": "uuid...", "name": null}}]}
+```
+
+El formato con `resizeNode` es el que usa el editor de Metabase cuando un usuario inserta una card manualmente — sin él, la card se renderiza diminuta.