feat(banner): add pf-v6-banner

[zeroedin]

Summary

Closes #2983

• Adds pf-v6-banner element ported from pf-v5-banner and aligned with the React v6 Banner component
• Replaces v5 variant attribute with separate color (8 decorative colors) and status (5 semantic statuses) attributes, matching React's split API
• Adds screen-reader-text attribute for visually-hidden status announcements (WCAG 1.3.1)
• Retains sticky attribute (maps to React isSticky)
• Removes v5 icon attribute/slot — icons are now composed in the default slot, matching React v6
• All CSS uses v6 design tokens with hex fallbacks via light-dark() for standalone usage

Deviations from React

• Status demo uses pf-v5-icon: The status demo composes icons in the default slot using pf-v5-icon because pf-v6-icon is not yet merged to staging/pfv6. Once pf-v6-icon lands, the status demo should be updated to use pf-v6-icon with the rh-ui-*-fill icon set to match the React demos visually.
• Sticky demo: React has isSticky as a prop but no dedicated demo on patternfly.org. We include a standalone sticky demo since the behavior requires scrollable content to verify — this was carried forward from the v5 element.

Test plan

• 36 unit tests passing (instantiation, upgrade, all 8 colors, all 5 statuses, sticky positioning, slotted link a11y, screen-reader-text presence/absence)
• Visual comparison against patternfly.org in both light and dark mode
• /review-a11y — no critical issues
• /review-api — no critical issues
• /review-demos — all demos match patternfly.org parity
• cem health — 87/100 (above 80% threshold)
• Verify demos at http://localhost:8000/elements/banner/demo/{slug}?rendering=chromeless

🤖 Generated with Claude Code

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More Info

{
  "valid": true,
  "errors": [],
  "warnings": [],
  "input": "feat(banner): add pf-v6-banner"
}

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