Area: src/lib/components/ExportModal.svelte
Severity: High

Problem

While PDF / Fountain / plain-text export is running, the only feedback is the button
label changing to Exporting.... On a long screenplay this takes several seconds and
the app looks frozen — no spinner, no progress bar, no cancel button.

Suggested fix

• Replace the "Exporting..." button label with an inline spinner + progress text.
• Consider indeterminate progress bar at the top of the modal.
• (Stretch) Offer a Cancel button that aborts the in-flight invoke.