fix(a11y): omit unset semantic attributes

[Banegasn]

Fixes #21

Summary

• omit unset optional ARIA, role, tabindex, and IDREF attributes with Lit nothing/ifDefined across affected component templates
• preserve visible and slotted control names; add the reusable browser regression helper and coverage for buttons, chips, cards, and list items
• make unnamed progress and decorative/hidden badges absent from the accessibility tree; retain named determinate and indeterminate progress semantics
• add focused tests for optional menu labels, menu IDREFs, and radio IDREF absence

Acceptance mapping

• Optional semantic attributes are omitted rather than rendered empty or as optional false states.
• Visible-label buttons, chips, cards, and items have browser accessibility coverage without aria-label masking their content.
• IDREF attributes are omitted when unset; existing dialog/menu contracts continue to generate valid targets.
• Decorative and hidden badges are removed from the accessibility tree; named badges expose a status.
• Named determinate/indeterminate progress semantics are correct; unnamed progress is decorative.
• test/semantic-attributes.ts establishes the browser regression convention.

Validation

• pnpm typecheck
• pnpm lint
• focused browser tests across Chromium, Firefox, and WebKit for button, chip, badge, list, fab-menu, and split-button
• pnpm test exercises all component suites successfully but the existing Angular shell test fails under the available Node 26 runtime because localStorage is undefined.