Toast titles use a hard-coded h1 heading level

[vvallalta-code]

Summary

Every toast title is rendered as an h1, regardless of the surrounding document hierarchy. Transient notifications should not introduce multiple or contextually incorrect level-one headings.

Location

• Package: @paperbits/core
• Template: src/ko/ui/defaultViewManager.html
• Current element: <h1 class="toast-header" data-bind="text: title"></h1>

Expected behavior

Toast titles use context-appropriate semantics without disrupting the page heading hierarchy. The existing alert/live-region announcement behavior remains intact.

Acceptance criteria

• Replace the hard-coded h1 with a context-appropriate heading or non-heading title contract.
• Preserve role="alert", live-region behavior, styling, and toast commands.
• Confirm toast content is announced once and does not alter the document outline incorrectly.
• Add or update an accessibility regression test where practical.

Tracking: Azure DevOps 30093183