feat(materials): show save progress overlay while optimizing images

Block the editor with a spinner and percent stages during material upsert so long image optimization is visible and non-interactive.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/shared/ipc/contracts.ts

@@ -109,6 +109,7 @@ export const ipcChannels = {
     importZipProgress: 'project.importZipProgress',
     exportZipProgress: 'project.exportZipProgress',
     scenePreviewImportProgress: 'project.scenePreviewImportProgress',
+    materialUpsertProgress: 'project.materialUpsertProgress',
   },
   windows: {
     openMultiWindow: 'windows.openMultiWindow',
@@ -191,6 +192,12 @@ export type ScenePreviewImportEvent = {
   message?: string;
 };
 
+export type MaterialUpsertProgressEvent = {
+  percent: number;
+  stage: string;
+  detail?: string;
+};
+
 export type UpdaterCheckResponse =
   | { outcome: 'not_packaged' }
   | { outcome: 'no_license' }
@@ -231,6 +238,7 @@ export type IpcEventMap = {
   [ipcChannels.project.importZipProgress]: ZipProgressEvent;
   [ipcChannels.project.exportZipProgress]: ZipProgressEvent;
   [ipcChannels.project.scenePreviewImportProgress]: ScenePreviewImportEvent;
+  [ipcChannels.project.materialUpsertProgress]: MaterialUpsertProgressEvent;
   [ipcChannels.updater.progress]: UpdaterProgressEvent;
 };