accessibility: add aria-live region announcements for simulation speed changes

[SourabhX16]

Problem Statement

Changing simulation speed multiplier (1x, 10x, 100x) updates UI text without screen reader announcement.

Why It Matters

Visually impaired users cannot tell what simulation speed rate is active.

Expected Behaviour

Speed multiplier button clicks should update an aria-live='polite' region (e.g. 'Simulation speed set to 10x').

Acceptance Criteria

• Screen reader live region announces simulation speed changes.
• Polite priority configured.
• Clear speed rate communicated.

Likely Affected Files / Components

• src/components/Header.tsx

[mittalsonal]

Hi maintainers, I would like to work on this issue under GSSoC '26.

Proposed Solution

• Inspect the simulation speed controls in src/components/Header.tsx and identify where the active speed multiplier is updated.
• Add a visually hidden aria-live=polite status region tied to simulation speed changes.
• Update the announcement text on speed button clicks, e.g. Simulation speed set to 10x, without changing the visual UI behavior.
• Add or update focused tests for the announcement text if the existing test setup covers the Header controls.

Please assign this to @mittalsonal if it is available.

[SourabhX16]

Assigned @mittalsonal