Suggest ffdelay-style filenames on export (_delayedNms)

Export used to suggest "<name>_synced<ext>", losing the offset value
itself. Restored the original ffdelay script's naming convention
(_delayed500ms / _delayed-500ms) so the applied offset is visible in
the filename, matching what the CLI tool already did before this GUI
existed.

main.py

@@ -500,7 +500,11 @@ class MainWindow(QMainWindow):
         delay_ms = self.override_spinbox.value()
 
         input_p = Path(self.input_path)
-        suggested = str(input_p.with_name(f"{input_p.stem}_synced{input_p.suffix}"))
+        # Matches the original ffdelay script's naming convention
+        # (e.g. "_delayed500ms" / "_delayed-500ms") rather than inventing
+        # a new one.
+        delayed_str = f"{int(round(delay_ms))}"
+        suggested = str(input_p.with_name(f"{input_p.stem}_delayed{delayed_str}ms{input_p.suffix}"))
         output_path, _ = QFileDialog.getSaveFileName(self, "Export synced file", suggested)
         if not output_path:
             return