[codex] Bucket autosave status announcements

[ashfame]

What changed

This is the minimal fix for #3815. The save/autosave indicator keeps the existing role="status" live region, but the accessible aria-label no longer changes for every visual progress percentage. The visible progress ring still updates with exact progress, while the spoken label is bucketed to 0%, 25%, 50%, 75%, and 100%.

The existing Playwright autosave status sampling was updated to assert that progress labels only use those buckets.

Approach

The implementation adds a small getAnnouncedProgressPercent() helper and uses it only for the aria-label. getProgressPercent() is unchanged and continues to drive the visual ring.

Pros

• Smallest code change.
• Low behavioral risk because it preserves the current role="status" structure.
• Reduces screen reader announcement frequency from every percent to at most five progress labels.
• Does not affect visual progress fidelity.

Cons

• Still uses a live status region to expose progress.
• The accessible label is intentionally stale between 25% buckets.
• Screen reader users cannot query the exact current percentage from the live region unless it happens to be on a bucket.
• This mitigates the verbosity but does not model the indicator as a semantic progressbar.

Validation

• npm exec nx -- run playground-website:typecheck
• npm exec nx -- run playground-website:lint