[feat]: Create <pf-v6-skip-to-content> element #2941

Summary

Create `` to implement the PatternFly v6 Skip to content component.

Visually hidden link that becomes visible on focus, allowing keyboard users to skip navigation and jump to main content.

Prior Art

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` SkipToContent
• 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 `href` - anchor pointing to main content `id` (e.g. `"#main-content"`); required
• Renders as a `` with `href`; visually hidden until focused (CSS clip/transform trick)
• MUST be the first focusable element in the page - place it before all navigation
• On focus: element becomes visible, positioned absolutely in top-left corner
• Click/Enter: follows the href anchor, moving focus to main content
• No complex state; pure CSS show-on-focus with single `` element

Checklist

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
• Keyboard tab order verified (first focusable element)

Reviews

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

Ship

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