Render the scenario export workbook with a sheet per scenario 🟩

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/xlsx/scenario_export_workbook.py

@@ -8,8 +8,11 @@ dynamic number of scenario sheets is handled natively.
 
 from __future__ import annotations
 
+from io import BytesIO
 from typing import Sequence
 
+from openpyxl import Workbook
+
 from domain.scenario_export.scenario_sheet import ExportSheet
 
 
@@ -17,4 +20,17 @@ def render_workbook(sheets: Sequence[tuple[str, ExportSheet]]) -> bytes:
     """Render the scenario sheets into a single branded ``.xlsx`` as bytes. Each
     tuple is a Scenario name and its shaped sheet; sheet order follows the input
     (the requested ``scenario_ids`` order)."""
-    raise NotImplementedError
+    workbook = Workbook()
+    default = workbook.active
+    if default is not None:
+        workbook.remove(default)
+
+    for name, sheet in sheets:
+        worksheet = workbook.create_sheet(title=name)
+        worksheet.append(list(sheet.columns))
+        for row in sheet.rows:
+            worksheet.append([row.get(column, "") for column in sheet.columns])
+
+    buffer = BytesIO()
+    workbook.save(buffer)
+    return buffer.getvalue()