fix: render calendar overlap conflicts safely

src/pages/CalendarPage.tsx

@@ -252,6 +252,17 @@ export default function CalendarPage() {
       const detail = err.response?.data?.detail
       if (typeof detail === 'string' && detail.toLowerCase().includes('overlap')) {
         setError(`⚠️ Overlap conflict: ${detail}`)
+      } else if (detail && typeof detail === 'object') {
+        const message = typeof detail.message === 'string' ? detail.message : 'Save failed'
+        const conflicts = Array.isArray(detail.conflicts) ? detail.conflicts : []
+        if (conflicts.length > 0) {
+          const summary = conflicts
+            .map((conflict: any) => `${conflict.slot_type || 'slot'} at ${conflict.scheduled_at || 'unknown time'}`)
+            .join(', ')
+          setError(`⚠️ ${message}: ${summary}`)
+        } else {
+          setError(`⚠️ ${message}`)
+        }
       } else {
         setError(detail || 'Save failed')
       }