feat(editor): show scene preview immediately and optimize in background

Return control after copying the original asset, then run image optimization
and thumbnail generation in the background with IPC progress updates.
Block duplicate preview uploads and scene creation while requests are in flight.

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

app/main/project/zipStore.legacyContract.test.ts

@@ -28,9 +28,25 @@ void test('zipStore: openProjectById flushes pending saveNow before cache reset'
   const src = fs.readFileSync(path.join(here, 'zipStore.ts'), 'utf8');
   // When switching projects we rm cacheDir and unzip zip; ensure pending debounced pack is flushed first.
   assert.match(src, /async openProjectById/);
+  assert.match(src, /enqueueOpenProject/);
+  assert.match(src, /openProjectByIdInner/);
   assert.match(src, /if \(this\.openProject\)\s*\{\s*await this\.saveNow\(\);\s*\}/);
+  assert.match(src, /await this\.drainSavePipeline\(\)/);
   assert.match(src, /await fs\.rm\(cacheDir, \{ recursive: true, force: true \}\)/);
-  assert.match(src, /await unzipToDir\(zipPath, cacheDir\)/);
+  assert.match(src, /await unzipToDir\(zipPath, cacheDir/);
+});
+
+void test('zipStore: openProjectById skips re-unzip when project is already open', () => {
+  const src = fs.readFileSync(path.join(here, 'zipStore.ts'), 'utf8');
+  assert.match(src, /if \(this\.openProject\?\.id === projectId\)\s*\{\s*return this\.openProject\.project;\s*\}/);
+});
+
+void test('zipStore: pack and open operations are serialized', () => {
+  const src = fs.readFileSync(path.join(here, 'zipStore.ts'), 'utf8');
+  assert.match(src, /private packChain: Promise<void>/);
+  assert.match(src, /private openChain: Promise<void>/);
+  assert.match(src, /enqueuePack/);
+  assert.match(src, /enqueueOpenProject/);
 });
 
 void test('zipStore: exportProjectZipToPath flushes saveNow for currently open project', () => {