refactor(frontend): migrate off deprecated Ant Design 6 props

The repo's type-aware deprecation sweep (eslint.deprecated.config.js) reported fourteen findings; it now reports zero. Alert message becomes title and closable+onClose becomes closable.onClose; Select optionFilterProp moves into showSearch.optionFilterProp and suffixIcon becomes suffix; Drawer width becomes size; Progress trailColor becomes railColor. Behavior is unchanged apart from a few single-mode selects gaining type-to-filter, which the old prop already implied.

frontend/src/pages/inbounds/clients/AttachClientsModal.tsx

@@ -203,7 +203,7 @@ export default function AttachClientsModal({
           onChange={setTargetIds}
           options={targetOptions}
           placeholder={t('pages.inbounds.attachClientsTargets')}
-          optionFilterProp="label"
+          showSearch={{ optionFilterProp: 'label' }}
         />
       )}
     </Modal>

frontend/src/pages/inbounds/clients/AttachExistingClientsModal.tsx

@@ -203,7 +203,7 @@ export default function AttachExistingClientsModal({
                     options={groupOptions}
                     placeholder={t('pages.clients.group')}
                     style={{ minWidth: 160 }}
-                    optionFilterProp="label"
+                    showSearch={{ optionFilterProp: 'label' }}
                   />
                 )}
               </Space>