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

tools/project-converter/src/preload.cjs

@@ -0,0 +1,13 @@
+const { contextBridge, ipcRenderer } = require('electron');
+
+contextBridge.exposeInMainWorld('converter', {
+  pickInputZip: () => ipcRenderer.invoke('converter.pickInputZip'),
+  pickOutputZip: (inputPath) => ipcRenderer.invoke('converter.pickOutputZip', { inputPath }),
+  convert: ({ inputPath, outputPath }) =>
+    ipcRenderer.invoke('converter.convert', { inputPath, outputPath }),
+  onLog: (cb) => {
+    ipcRenderer.removeAllListeners('converter.log');
+    ipcRenderer.on('converter.log', (_e, { line }) => cb(line));
+  },
+});
+