fix(export): label synthetic ordinal '# Days Reach (ordinal)' to avoid collision with same-named daily field

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/tests/ExportDataModal.test.jsx

@@ -96,7 +96,7 @@ describe('ExportDataModal', () => {
     await waitFor(() => expect(screen.getByText(/2 rows/i)).toBeInTheDocument());
     fireEvent.click(screen.getByText('Export CSV'));
     const text = await readBlobText(dl.getBlob());
-    expect(text).toBe('Data,Total attempts\n\n# Days Reach,Alpha,Beta\n1,5,9\n2,7,');
+    expect(text).toBe('Data,Total attempts\n\n# Days Reach (ordinal),Alpha,Beta\n1,5,9\n2,7,');
     await dl.restore();
   });
 

frontend/tests/dataExport.test.js

@@ -281,7 +281,7 @@ describe('buildSubjectSeriesMatrix', () => {
       { xField: '__days__', dataParam: totalParam, groupField: '__none__' },
       { statuses: ssStatuses, animals: ssAnimals, dailyTemplate: [] },
     );
-    expect(m.corner).toBe('# Days Reach');
+    expect(m.corner).toBe('# Days Reach (ordinal)');
     expect(m.rows.map((r) => r.member.label)).toEqual(['1', '2']);
     expect(m.rows[0].values).toEqual([5, 9]);
     expect(m.rows[1].values).toEqual([7, '']);