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/optimizeImageImport.lib.d.mts

@@ -0,0 +1,14 @@
+import type { Buffer } from 'node:buffer';
+
+export type OptimizeImageImportResult = {
+  buffer: Buffer;
+  mime: string;
+  ext: string;
+  width: number;
+  height: number;
+  passthrough: boolean;
+};
+
+export function optimizeImageBufferVisuallyLossless(
+  input: Buffer,
+): Promise<OptimizeImageImportResult>;