♿️(frontend) fix sidebar resize handle for screen readers

[Ovgodd]

Purpose

Fix left sidebar keyboard resize with a screen reader on, and improve SR output plus step size.

Proposal

• Replace the default separator role with slider so that, when the handle is focused, screen readers pass Left/Right to the app instead of using them for reading (known issue with separator in NVDA).
• from aria-valuenow into aria-valuetext (width in px).
• Use keyboardResizeBy={1} for smaller steps.

[github-actions]

Size Change: +214 B (+0.01%)

Total Size: 4.23 MB

Filename	Size	Change
apps/impress/out/_next/static/3574adc1/_buildManifest.js	0 B	-905 B (removed)	🏆
apps/impress/out/_next/static/f3d1265a/_buildManifest.js	904 B	+904 B (new file)	🆕

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