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

Start by reading .claude/ADVICE.md and the existing elements/pf-v5-jump-links/ implementation, then inspect elements/package.json and the referenced docs and framework-integration snippets. Done means a PatternFly v6 component and sub-components with the listed API, demos, public API and a11ySnapshot tests, review checks, a changeset, and a PR targeting staging/pfv6.

Summary

Update `` to implement the PatternFly v6 Jump links component.

In-page navigation that tracks scroll position and highlights the active section. Supports vertical and horizontal layouts.

Prior Art

Sub-components

• `` - Individual section link
• `` - Nested list for sub-sections

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` JumpLinks
• 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` - vertical layout; map to `vertical` attribute
• React `label` - visible section label above links (e.g. "ON THIS PAGE")
• React `offset` - scroll offset in px to account for sticky headers; map to `offset` attribute
• React `scrollableSelector` - CSS selector for scrollable container; default window; map to `scrollable-selector` attribute
• React `activeIndex` (controlled) - use `IntersectionObserver` for auto-detection; expose `active-index` attribute for controlled mode
• `JumpLinksItem` has `href` (anchor link), `isActive`, `onClick` - use `` slots; active driven by scroll observation
• `JumpLinksList` for nested sub-sections (two-level depth)
• SSR: `IntersectionObserver` setup in `updated` with `isServer` guard

Checklist

Rename

• Delete `elements/pf-v5-jump-links/`
• 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`)