feat(project): optimize image imports and converter

- Optimize imported scene preview images (smart WebP/JPEG/PNG, preserve alpha, keep pixel size)

- Update converter to re-encode existing image assets with same algorithm

- Improve import/export progress overlay and reduce presentation slide stutter

Made-with: Cursor

app/main/project/assetPrune.test.ts

@@ -14,6 +14,7 @@ void test('collectReferencedAssetIds: превью, видео и аудио', (
     scenes: {
       s1: {
         previewAssetId: 'pr' as AssetId,
+        previewThumbAssetId: 'th' as AssetId,
         media: {
           videos: ['v1' as AssetId],
           audios: [{ assetId: 'a1' as AssetId, autoplay: true, loop: true }],
@@ -23,7 +24,7 @@ void test('collectReferencedAssetIds: превью, видео и аудио', (
     campaignAudios: [{ assetId: 'ca1' as AssetId, autoplay: true, loop: true }],
   } as unknown as Project;
   const s = collectReferencedAssetIds(p);
-  assert.deepEqual([...s].sort(), ['a1', 'ca1', 'pr', 'v1'].sort());
+  assert.deepEqual([...s].sort(), ['a1', 'ca1', 'pr', 'th', 'v1'].sort());
 });
 
 void test('reconcileAssetFiles: снимает осиротевшие assets и удаляет файлы', async () => {