[a11y][critical] Timeline collapse: Toggle uses aria-pressed, disclosure needs aria-expanded

[fedorovvvv]

Source: PRD-018 SC-2 audit, finding [Logic-C2].

template/src/widgets/timeline/ui/Timeline.svelte:151-160

The Timeline's collapse control was previously a <button> with aria-expanded={!collapsed} — disclosure semantics. Migration replaced it with <Toggle pressed={!snapshotStore.collapsed}>. Toggle communicates aria-pressed (a two-state button), which is not the same as aria-expanded (a disclosure widget that controls visibility of another region).

Screen readers will now announce "toggle button, pressed" instead of "expanded" / "collapsed".

Fix

Replace <Toggle> with <Button> plus an explicit aria-expanded={!collapsed} aria-controls="timeline-body" — OR extend shared/ui/toggle/Toggle.svelte to accept and forward an aria-expanded prop (and document on /playground that pressed-as-disclosure is a supported pattern).

Acceptance

• The collapse control announces "expanded" / "collapsed" with screen readers.
• aria-controls points to the Timeline body region for navigation.

Audit traceability

• Reviewer: Logic & Correctness, score 7/10
• File: template/src/widgets/timeline/ui/Timeline.svelte

[fedorovvvv]

Fixed in branch `develop` as part of PRD-019 Wave 1.

What changed (template/src/widgets/timeline/ui/Timeline.svelte)

• Replaced <Toggle pressed={…}> (which carried aria-pressed) with <Button variant="ghost" size="sm"> that exposes aria-expanded={!collapsed} and aria-controls="timeline-body".
• Dropped the Toggle import in this file.

Browser-verified accessibility tree

button.timeline-toggle
  aria-expanded="true"
  aria-controls="timeline-body"
  aria-pressed=null

✅ Disclosure semantics restored; screen readers announce "expanded"/"collapsed".

Acceptance

• The collapse control announces "expanded"/"collapsed" (no longer "pressed").
• aria-controls points to the Timeline body region.
• npm run check clean.

Tracking PR: pending (will batch with rest of #99 follow-ups).

[fedorovvvv]

Resolved by PR #100 (merged into develop as merge commit 6f498b9). Will reach main with the next release/v* cycle.