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

Start with .claude/ADVICE.md and the existing elements/pf-v5-progress-stepper/ implementation, then review elements/package.json and the referenced docs and framework-integration snippets. Done means a PFv6 progress stepper and step with the specified API, accessibility assertions, demos, styling, reviews, changeset, and a PR targeting staging/pfv6.

Summary

Update `` to implement the PatternFly v6 Progress stepper component.

Multi-step progress indicator showing completed, current, and pending steps with status icons.

Prior Art

Sub-components

• `` - Individual step with status and description

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` ProgressStepper
• 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 `isVertical` - stacks steps vertically; map to `vertical` attribute
• React `isCompact` - reduced spacing; map to `compact` attribute
• React `isCenterAligned` - centers step labels; map to `center` attribute
• `ProgressStepperStep` props: `variant` (`default`, `info`, `warning`, `success`, `danger`), `isCurrent`, `id`, `titleId`, `description`, `popoverRender` (info popover on step)
• ARIA: `role="list"` on container, `role="listitem"` on steps; `aria-label` on stepper
• `isCurrent` step should have `aria-current="step"`
• Icons come from `` - dependency

Checklist

Rename

• Delete `elements/pf-v5-progress-stepper/`
• 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`)