feat(fusion_accounting_reports): XLSX export wizard

Adds a TransientModel wizard fusion.xlsx.export.wizard that lets users
pick a report type, date range, and comparison mode, then runs the
engine and produces an XLSX via xlsxwriter (in-memory).

The wizard exposes a download field that becomes available after export
finishes. Works on P&L, Balance Sheet, Trial Balance, and General Ledger.
Comparison columns are written when the engine returns a comparison_period
in the result.

Also wires the controller's /fusion/reports/export_xlsx endpoint to drive
the wizard and return base64-encoded XLSX bytes (replaces the not_implemented
placeholder).

Tests: 2 new (test_xlsx_export.py) + 1 controller test updated. Manifest
declares xlsxwriter as an external_dependency.

Made-with: Cursor

fusion_accounting_reports/controllers/reports_controller.py

@@ -234,7 +234,15 @@ class FusionReportsController(http.Controller):
     @http.route('/fusion/reports/export_xlsx', type='jsonrpc', auth='user')
     def export_xlsx(self, report_type, date_from, date_to,
                     comparison='none', company_id=None):
+        wizard = request.env['fusion.xlsx.export.wizard'].create({
+            'report_type': report_type,
+            'date_from': _parse_date(date_from),
+            'date_to': _parse_date(date_to),
+            'comparison': comparison,
+        })
+        wizard.action_export()
         return {
-            'status': 'not_implemented',
-            'message': 'XLSX export shipping in Task 35',
+            'status': 'ok',
+            'xlsx_base64': wizard.xlsx_file.decode('ascii') if wizard.xlsx_file else '',
+            'filename': wizard.xlsx_filename,
         }