fix(spool-assign): defer MQTT for empty AMS slot, replay on physical insert

The SpoolBuddy "weigh-then-assign" workflow tried to configure an empty AMS
  slot at assign time, but Bambu firmware silently drops ams_filament_setting
  and extrusion_cali_sel for unloaded slots — the MQTT calls completed and the
  modal closed, yet BambuStudio kept showing the slot as default-PLA forever.

  assign_spool now detects an empty target slot (fingerprint_type empty) and
  persists the SpoolAssignment without publishing MQTT, returning a new
  pending_config flag so the frontend can swap "Assigned!" for "Slot will
  configure when you insert the spool." on_ams_change watches for the slot
  to load (state == 11, which fires for 3rd-party tags too even when
  tray_type stays empty) and replays the deferred ams_filament_setting +
  extrusion_cali_sel — including the printer-kp realignment that converts
  PFUS-prefix cloud user presets to the P-prefix local-preset filament_id
  the slicer actually accepts.

  The full assign-time MQTT block was extracted into
  apply_spool_to_slot_via_mqtt so both the assign endpoint and the
  on_ams_change replay path use the same resolution logic; the helper takes
  ~270 lines of duplication out of assign_spool.

frontend/src/api/client.ts

@@ -2346,6 +2346,7 @@ export interface SpoolAssignment {
   fingerprint_type: string | null;
   spool?: InventorySpool | null;
   configured: boolean;
+  pending_config?: boolean;  // Slot was empty at assign time; will configure on insert
   created_at: string;
   ams_label?: string | null;  // User-defined friendly name for the AMS unit
 }

frontend/src/components/spoolbuddy/AssignToAmsModal.tsx

@@ -167,27 +167,37 @@ export function AssignToAmsModal({ isOpen, onClose, spool, printerId }: AssignTo
   }, [isDualNozzle, amsExtruderMap]);
 
   // Assign spool to AMS slot — single API call, backend handles both
-  // DB record AND MQTT auto-configuration (same as SpoolStation).
+  // DB record AND MQTT auto-configuration (same as SpoolStation). When the
+  // target slot is currently empty, the backend persists the assignment and
+  // skips the MQTT publish (firmware drops it anyway); on_ams_change re-fires
+  // the full configuration when filament is later inserted. The response's
+  // `pending_config` flag distinguishes that from the immediate-apply path
+  // so we can adjust the success toast.
   const configureMutation = useMutation({
     mutationFn: async ({ amsId, trayId }: { amsId: number; trayId: number }) => {
       if (!printerId) throw new Error('No printer selected');
 
-      await api.assignSpool({
+      return await api.assignSpool({
         spool_id: spool.id,
         printer_id: printerId,
         ams_id: amsId,
         tray_id: trayId,
       });
-
-      // Slot preset mapping is now saved by the backend in assign_spool()
-      // after successful MQTT configuration, using the authoritative
-      // slicer_filament_name from the spool record.
     },
-    onSuccess: () => {
+    onSuccess: (assignment) => {
       setStatusType('success');
-      setStatusMessage(t('spoolbuddy.modal.assignSuccess', 'Assigned!'));
+      if (assignment?.pending_config) {
+        setStatusMessage(
+          t(
+            'spoolbuddy.modal.assignPendingInsert',
+            'Assigned. Slot will configure when you insert the spool.',
+          ),
+        );
+      } else {
+        setStatusMessage(t('spoolbuddy.modal.assignSuccess', 'Assigned!'));
+      }
       queryClient.invalidateQueries({ queryKey: ['slotPresets'] });
-      setTimeout(() => onClose(), 1500);
+      setTimeout(() => onClose(), assignment?.pending_config ? 2500 : 1500);
     },
     onError: (err) => {
       setStatusType('error');

frontend/src/i18n/locales/de.ts

@@ -5032,6 +5032,7 @@ export default {
       assign: 'Zuweisen',
       assigning: 'Zuweisen...',
       assignSuccess: 'Zugewiesen!',
+      assignPendingInsert: 'Zugewiesen. Slot wird beim Einsetzen der Spule konfiguriert.',
       assignError: 'Fehler beim Zuweisen. Bitte erneut versuchen.',
       noPrinterSelected: 'Drucker auswählen...',
       noAmsDetected: 'Kein AMS an diesem Drucker erkannt',

frontend/src/i18n/locales/en.ts

@@ -5041,6 +5041,7 @@ export default {
       assign: 'Assign',
       assigning: 'Assigning...',
       assignSuccess: 'Assigned!',
+      assignPendingInsert: 'Assigned. Slot will configure when you insert the spool.',
       assignError: 'Failed to assign spool. Please try again.',
       noPrinterSelected: 'Select a printer...',
       noAmsDetected: 'No AMS detected on this printer',

frontend/src/i18n/locales/fr.ts

@@ -5020,6 +5020,7 @@ export default {
       assign: 'Assigner',
       assigning: 'Attribution...',
       assignSuccess: 'Assigné !',
+      assignPendingInsert: 'Assigné. Le slot sera configuré lors de l\'insertion de la bobine.',
       assignError: 'Échec de l\'attribution de la bobine. Veuillez réessayer.',
       noPrinterSelected: 'Sélectionner une imprimante...',
       noAmsDetected: 'Aucun AMS détecté sur cette imprimante',

frontend/src/i18n/locales/it.ts

@@ -5019,6 +5019,7 @@ export default {
       assign: 'Assegna',
       assigning: 'Assegnazione...',
       assignSuccess: 'Assegnato!',
+      assignPendingInsert: 'Assegnato. Lo slot verrà configurato all\'inserimento della bobina.',
       assignError: 'Impossibile assegnare la bobina. Riprovare.',
       noPrinterSelected: 'Seleziona una stampante...',
       noAmsDetected: 'Nessun AMS rilevato su questa stampante',

frontend/src/i18n/locales/ja.ts

@@ -5032,6 +5032,7 @@ export default {
       assign: '割り当て',
       assigning: '割り当て中...',
       assignSuccess: '割り当て完了！',
+      assignPendingInsert: '割り当てました。スプールを挿入したときにスロットが設定されます。',
       assignError: 'スプールの割り当てに失敗しました。再試行してください。',
       noPrinterSelected: 'プリンターを選択...',
       noAmsDetected: 'このプリンターにAMSが検出されません',

frontend/src/i18n/locales/pt-BR.ts

@@ -5019,6 +5019,7 @@ export default {
       assign: 'Atribuir',
       assigning: 'Atribuindo...',
       assignSuccess: 'Atribuído!',
+      assignPendingInsert: 'Atribuído. O slot será configurado quando você inserir o carretel.',
       assignError: 'Falha ao atribuir carretel. Tente novamente.',
       noPrinterSelected: 'Selecionar uma impressora...',
       noAmsDetected: 'Nenhum AMS detectado nesta impressora',

frontend/src/i18n/locales/zh-CN.ts

@@ -5019,6 +5019,7 @@ export default {
       assign: '分配',
       assigning: '分配中...',
       assignSuccess: '已分配！',
+      assignPendingInsert: '已分配。插入耗材后将配置槽位。',
       assignError: '分配耗材失败。请重试。',
       noPrinterSelected: '选择打印机...',
       noAmsDetected: '此打印机未检测到 AMS',

frontend/src/i18n/locales/zh-TW.ts

@@ -5019,6 +5019,7 @@ export default {
       assign: '分配',
       assigning: '分配中...',
       assignSuccess: '已分配！',
+      assignPendingInsert: '已分配。插入耗材後將設定槽位。',
       assignError: '分配耗材失敗。請重試。',
       noPrinterSelected: '選擇印表機...',
       noAmsDetected: '此印表機未偵測到 AMS',