♿️(frontend) add sr-only format to export download button

[Ovgodd]

Purpose

Help screen reader users know which format will be exported before they click. Today they only hear "Download" and can't tell if it's PDF, DOCX, etc.

Proposal

• Add the selected format to the download button’s aria-label (e.g. "Download PDF") for screen readers
• Remove the redundant aria-label that repeated the visible text
• Simplify the code by using one shared list of format options

[github-actions]

Size Change: +7 B (0%)

Total Size: 4.23 MB

Filename	Size	Change
apps/impress/out/_next/static/56355b45/_buildManifest.js	0 B	-905 B (removed)	🏆
apps/impress/out/_next/static/fdc1d82d/_buildManifest.js	905 B	+905 B (new file)	🆕

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