[feat]: Update <pf-v6-card> for PatternFly v6 #2986

Summary

Update `` to implement the PatternFly v6 Card component.

Content container with header, title, body, and footer sections. Supports selectable, expandable, and full-height variants.

Prior Art

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Card
• 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 `isCompact`, `isFlat`, `isRounded`, `isFullHeight`, `isPlain` - each maps to a boolean attribute
• Selectable card: React `isSelectable`, `isSelected`, `hasSelectableInput`, `selectableInputAriaLabel` - complex interaction; selectable card contains a hidden checkbox/radio; consider whether this warrants a separate element or is handled via attributes
• Clickable card: React `isClickable`, `isSelectableRaised`, `isDisabledRaised` - entire card is an interactive element; needs careful ARIA (role="article" + button child, or role="link")
• React sub-components: `CardTitle`, `CardHeader`, `CardBody`, `CardFooter`, `CardActions` - use named slots
• `CardActions` contains buttons/links within the header - slot in header area
• Selectable/clickable variants need keyboard interaction (Enter/Space to select)

Checklist

Rename

• Delete `elements/pf-v5-card/`
• 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`)