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/src/components/ExperimentCalendar.jsx

@@ -72,10 +72,16 @@ function DayPanel({ date, animals, allStatuses, template, experimentId, selected
 
   const fieldLabel = fieldOptions.find((f) => f.value === selectedField)?.label;
 
+  // Only show animals that have a status record for this day
+  const animalsWithData = animals.filter((a) => statusByAnimal[a.id]);
+
   return (
     <div className="space-y-3 max-h-[80vh] overflow-y-auto pr-1">
+      {animalsWithData.length === 0 && (
+        <p className="text-gray-400 text-sm py-2">No data recorded for this day.</p>
+      )}
       {/* Per-animal data for this day */}
-      {animals.map((animal) => {
+      {animalsWithData.map((animal) => {
         const existing = statusByAnimal[animal.id];
         const isEditing = editingAnimalId === animal.id;
         return (
@@ -93,7 +99,7 @@ function DayPanel({ date, animals, allStatuses, template, experimentId, selected
                   onClick={() => setEditingAnimalId(animal.id)}
                   className="text-xs text-blue-600 hover:text-blue-800 border border-blue-200 rounded px-2 py-0.5 hover:bg-blue-50 transition-colors"
                 >
-                  {existing ? 'Edit' : '+ Add'}
+                  Edit
                 </button>
               )}
             </div>
@@ -102,17 +108,12 @@ function DayPanel({ date, animals, allStatuses, template, experimentId, selected
                 animalId={animal.id}
                 experimentId={experimentId}
                 template={template}
-                existing={existing ? { ...existing, date: dateStr } : undefined}
-                onSuccess={(saved) => {
-                  if (existing) { onStatusChange(saved); } else { onStatusCreate(saved); }
-                  setEditingAnimalId(null);
-                }}
+                existing={{ ...existing, date: dateStr }}
+                onSuccess={(saved) => { onStatusChange(saved); setEditingAnimalId(null); }}
                 onCancel={() => setEditingAnimalId(null)}
               />
-            ) : existing ? (
-              <SubjectReadOnly status={existing} template={template} />
             ) : (
-              <p className="text-xs text-gray-400">No data recorded for this day.</p>
+              <SubjectReadOnly status={existing} template={template} />
             )}
           </div>
         );
@@ -132,9 +133,9 @@ function DayPanel({ date, animals, allStatuses, template, experimentId, selected
               <YAxis tick={{ fontSize: 11 }} allowDecimals={false} />
               <Tooltip />
               <Legend wrapperStyle={{ fontSize: 11 }} />
-              <Bar dataKey="total" name="Total" fill="#94a3b8" radius={[3, 3, 0, 0]} />
-              <Bar dataKey="success" name="Success" fill="#22c55e" radius={[3, 3, 0, 0]} />
-              <Bar dataKey="failure" name="Failure" fill="#f87171" radius={[3, 3, 0, 0]} />
+              <Bar dataKey="total" name="Total" fill="#94a3b8" />
+              <Bar dataKey="success" name="Success" fill="#22c55e" />
+              <Bar dataKey="failure" name="Failure" fill="#f87171" minPointSize={2} />
             </BarChart>
           </ResponsiveContainer>
           <div className="mt-2 flex flex-wrap gap-4">