feat: add placeholder support to EntityForm FieldDef

frontend/src/components/EntityForm.tsx

@@ -14,6 +14,7 @@ export interface FieldDef {
   required?: boolean
   type?: 'text' | 'select' | 'number'
   options?: { value: string | number; label: string }[]
+  placeholder?: string
 }
 
 interface Props {
@@ -67,6 +68,7 @@ export default function EntityForm({ open, title, fields, initialValues, onClose
                 value={values[f.name] ?? ''}
                 onChange={(e) => handleChange(f.name, e.target.value)}
                 size="small"
+                placeholder={f.placeholder}
               />
             )
           )}