feat(tableau): export Excel via DuckDB (AST->SQL) (#41)

Rewrite download_data to read filterModel/columnState from the AG Grid
component and add export_dataframe (compiles filterModel to SQL via
filtermodel_to_ast/ast_to_sql, builds ORDER BY, excludes hidden columns,
queries DuckDB via query_marches). Replaces the old Polars filter_query
pipeline tied to the removed DataTable.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_grid.py

@@ -1,4 +1,4 @@
-from src.utils.grid import fetch_grid_page, grid_column_defs
+from src.utils.grid import export_dataframe, fetch_grid_page, grid_column_defs
 
 
 def test_column_defs_have_field_and_filter():
@@ -40,3 +40,14 @@ def test_fetch_grid_page_filter_reduces_count():
 def test_fetch_grid_page_offset_slicing():
     rows, _ = fetch_grid_page(None, None, 0, 5)
     assert len(rows) <= 5
+
+
+def test_export_dataframe_excludes_hidden_columns():
+    df = export_dataframe(None, None, hidden_columns=["objet"])
+    assert "objet" not in df.columns
+
+
+def test_export_dataframe_applies_filter():
+    fm = {"objet": {"filterType": "text", "type": "contains", "filter": "zzzzzznope"}}
+    df = export_dataframe(fm, None, hidden_columns=[])
+    assert df.height == 0