fix: hide subjects with no data in day modal; fix failure bar rendering

- Day modal now only shows animals that have a status record for that day
- Removed '+ Add' button and 'No data' placeholder for absent subjects
- Fixed failure bars disappearing in recharts: removed radius from all bars,
  added minPointSize=2 on failure bar so zero-value bars remain visible

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/tests/ExperimentCalendar.test.jsx

@@ -227,8 +227,9 @@ describe('day click modal', () => {
     expect(screen.queryByRole('dialog')).not.toBeInTheDocument();
   });
 
-  it('shows all animals in the modal (with and without data)', async () => {
+  it('shows only animals with data — excludes subjects with no record that day', async () => {
     const dateStr = todayStr();
+    // Only Rat A has a record; Rat B does not
     const statuses = [
       makeStatus('a1000000-0000-0000-0000-000000000001', dateStr, { 'ww000000-0000-0000-0000-000000000099': '320' }),
     ];
@@ -239,7 +240,7 @@ describe('day click modal', () => {
     await waitFor(() => {
       const dialog = screen.getByRole('dialog');
       expect(within(dialog).getAllByText('Rat A').length).toBeGreaterThan(0);
-      expect(within(dialog).getAllByText('Rat B').length).toBeGreaterThan(0);
+      expect(within(dialog).queryAllByText('Rat B')).toHaveLength(0);
     });
   });
 });