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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[github-actions]

✅ Commitlint tests passed!

More Info

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

[github-actions]

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[github-actions]

SSR Test Run for 4a848b0: Report

[bennypowers]

this attribute name is vague: it's not immediately clear which text this is. only after reading the jsdoc does the user discover that this text describes the "type" of banner. "type", mind you, is not an attribute on this element, so that term is also vague. moreover, we use accessible-label as the name for screen reader texts in other elements.

@adamjohnson wdyt?

[bennypowers]

Suggested change

	return html`
	<div id="container" class=${classMap({
	[this.color ?? '']: !!this.color,
	[this.status ?? '']: !!this.status,
	})}>
	${!this.screenReaderText ? nothing
	const { color = '', status = '' } = this;
	return html`
	<div id="container" class="${classMap({ [color]: !!color, [status]: !!status })}">
	${!this.screenReaderText ? nothing

minor formatting nit

[bennypowers]

Suggested change

	${!this.screenReaderText ? nothing
	: html`<span class="sr-only">${this.screenReaderText}</span>`}
	<slot></slot>
	</div>
	<span class="sr-only" ?hidden="${!this.screenReaderText}">${this.screenReaderText}</span>
	<slot></slot>
	</div>