[A11Y] Missing ARIA labels across editor components

[adamghaleb]

Description

Only ~35 ARIA attribute occurrences exist across the entire editor. Most interactive elements lack proper accessibility attributes.

Missing ARIA Labels

• Timeline playhead: no `aria-label`
• Toolbar buttons: only `title` attributes (not ARIA)
• No `aria-live` regions for status updates (export progress, save status)
• Track mute/solo buttons: missing `aria-pressed`
• Selection box: no accessibility context
• No `role="progressbar"` on progress components
• Timeline structure not marked with ARIA regions

Expected

All interactive elements should have proper ARIA attributes for screen readers.

Files

• Most components in `apps/web/src/components/editor/`
• `apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx`
• `apps/web/src/components/editor/export-button.tsx`