[feat]: Update `<pf-v6-accordion>` for PatternFly v6

[bennypowers]

Summary

Update `` to implement the PatternFly v6 Accordion component.

Expandable content panels that allow users to show and hide sections of related content.

Prior Art

Source	Element	Status
PFE v4	``	Exists
cem	--	--
cockpit	--	--
chickadee	``	Exists

Sub-components

• `` - Toggle header for each panel
• `` - Expandable content area

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Accordion
• MAY adjust element API to leverage web platform strengths
• SHOULD maintain CSS custom property theming compatibility
• SHOULD expose useful CSS shadow parts

Element-specific considerations

• React `isBordered` - adds border around each panel; map to `bordered` attribute
• React `displaySize`: `default`, `lg` - larger toggle text; map to `size` attribute
• React `headingLevel`: `h1`-`h6` - sets heading element for toggle buttons; map to `heading-level`
• React `asDefinitionList` - renders as `

  `/`

  `/`

  ` instead of `

  `/`<h*>`/`

  ` - web component approach: use slots and reflect structure; probably skip this variant

• Single-expand vs multi-expand: React default is multi (all can be open); v5 element has `single` mode - verify v6
• `AccordionItem` wraps `AccordionToggle` + `AccordionContent` - consider if `pf-v6-accordion-item` sub-element is needed
• ARIA: toggle button has `aria-expanded`, `aria-controls` pointing to panel; panel has `id`

Checklist

Rename

• Delete `elements/pf-v5-accordion/`
• Update `elements/package.json` exports
• Update `eslint.config.js` ignore globs if applicable
• Update docs `_snippets/` and `framework-integration/` references

Implementation

• API per `.claude/ADVICE.md`
• CSS uses v6 tokens, logical properties, nesting
• `@summary` and JSDoc on element class

Demos

• Demos match patternfly.org naming/structure
• CSS custom properties match computed styles from patternfly.org (Chrome MCP)
• Visual parity verified via Chrome MCP

Tests

• Public API covered (attributes, properties, events, slots)
• `a11ySnapshot` assertions

Reviews

• `/review-api` passes
• `/review-demos` passes
• `/review-a11y` passes
• `eslint` and `stylelint` pass

Ship

• Add changeset
• PR targets `staging/pfv6` (NOT `main`)