feat(background-image): port pf-v5-background-image to pf-v6-background-image

[zeroedin]

Summary

• Removes <pf-v5-background-image>
• Ports <pf-v5-background-image> to <pf-v6-background-image> web component for PatternFly v6
• Simplified from 115 LOC to 36 LOC — removes responsive breakpoint image map in favor of a single src attribute (matching React v6)
• Uses --pf-v6-c-background-image--* design tokens matching PatternFly v6 SCSS
• Responsive sizing via clamp() with configurable min/width/max tokens
• Bidirectional support via :host(:dir(rtl)) (replaces SCSS bidirectional mixin)
• aria-hidden="true" on background container for WCAG compliance
• Replaces v5 JPEG demo images with v6 SVG pattern asset

Closes #2980

Intentional divergences from React

• --pf-v6-c-background-image--BackgroundPosition exposed as a public CSS custom property (React sets this internally via SCSS
  bidirectional mixin; shadow DOM prevents class-level overrides)

Test plan

• npm run test passes
• Demo renders correctly at localhost:8000 with ?rendering=chromeless
• Background image displays fixed behind page content
• src attribute sets the background image URL
• Removing src clears the background image
• Background color token applies when no image is set
• RTL layout positions image at bottom-left
• Background size tokens (--min-width, --width, --max-width) are respected
• Element is hidden from assistive technology (aria-hidden)

Assisted-By: Claude

Testing Instructions

Notes to Reviewers

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🦋 Changeset detected

Latest commit: d446c5d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@patternfly/elements	Major

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More Info

{
  "valid": true,
  "errors": [],
  "warnings": [],
  "input": "feat(background-image): port `pf-v5-background-image` to `pf-v6-background-image`"
}

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