Set taskbar progress on export

When the export is running, we could set the [taskbar progress bar using the corresponding electron api](https://www.electronjs.org/docs/latest/tutorial/progress-bar).

This would include:

1. Add a new [renderer ipc action](https://github.com/audapolis/audapolis/blob/main/app/ipc/ipc_renderer.ts) to send the progress
1. Add a new [main process ipc event handler](https://github.com/audapolis/audapolis/blob/main/app/ipc/ipc_main.ts) to receive the progress
2. Call this action from export function

Start with app/ipc/ipc_renderer.ts and app/ipc/ipc_main.ts, then locate the export function that should report progress. Add the renderer-to-main progress path and connect it to Electron's taskbar progress API. Done means an active export visibly updates the taskbar progress.

Written by the indexing model from the issue text.