feat(frontend): use Wails bindings for file I/O

Replace hidden file inputs and anchor downloads with native open/save
dialogs via a thin platform layer. WAV export sends base64 audio data to
the Go backend for writing to the user-chosen path.

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

frontend/bindings/sfxkeeb/fileservice.ts

@@ -24,8 +24,8 @@ export function OpenVideo(): $CancellablePromise<$models.VideoResult> {
     });
 }
 
-export function SaveAudio(data: string, defaultName: string): $CancellablePromise<void> {
-    return $Call.ByID(1785178400, data, defaultName);
+export function SaveAudio(dataBase64: string, defaultName: string): $CancellablePromise<void> {
+    return $Call.ByID(1785178400, dataBase64, defaultName);
 }
 
 export function SaveProject(content: string, defaultName: string): $CancellablePromise<void> {