feat(metabase): smartscalar KPI builders (sql + payload + dimension tag)

3 helpers puros para construir KPIs con display=smartscalar y comparacion
vs n-1 sin que Metabase v0.59 pida breakout temporal. Replican el patron
del dashboard Informe Lean (UNION ALL de 2 filas periodo/valor) y rellenan
la firma exacta de template-tags que el frontend MBQL5 acepta.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

python/functions/metabase/__init__.py

@@ -13,6 +13,7 @@ from .setup import metabase_setup
 from .maintenance import metabase_fix_null_ratio, metabase_pair_n_n1_columns
 from .metabase_mbql_validate import metabase_mbql_validate
 from .metabase_update_dashboard_safe import metabase_update_dashboard_safe
+from .smartscalar import metabase_smartscalar_kpi_sql, metabase_smartscalar_dimension_tag, metabase_smartscalar_kpi_payload
 
 __all__ = [
     "MetabaseClient",
@@ -38,4 +39,5 @@ __all__ = [
     "metabase_pair_n_n1_columns",
     "metabase_mbql_validate",
     "metabase_update_dashboard_safe",
+    "metabase_smartscalar_kpi_sql", "metabase_smartscalar_dimension_tag", "metabase_smartscalar_kpi_payload",
 ]