[feat]: Update <pf-v6-popover> for PatternFly v6 #3030

Summary

Update `` to implement the PatternFly v6 Popover component.

Rich content popup triggered by click, with header, body, footer, and close button. Supports multiple positions and auto-positioning.

Prior Art

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Popover
• 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

• Uses Floating UI for positioning (shared dep with tooltip)
• React `position`: 12 values (`top`, `top-start`, `top-end`, `bottom`, `bottom-start`, `bottom-end`, `left`, `left-start`, `left-end`, `right`, `right-start`, `right-end`, `auto`)
• React `headerContent`, `bodyContent`, `footerContent` - use named slots
• React `headerComponent`: `h1`-`h6` - heading level in header slot
• React `hasAutoWidth` - removes max-width constraint; map to `auto-width` attribute
• React `showClose` (default true) - whether to render close button; map to `no-close` attribute (opt-out)
• React `distance`, `minWidth`, `maxWidth` - CSS custom properties preferred
• React `flipBehavior` - Floating UI flip fallback positions
• React `alertSeverityVariant` - adds alert icon to header for status popovers; map to `alert` attribute
• Focus management: focus moves into popover on open; Escape closes and returns focus to trigger
• Trigger element: use `for` attribute or wrap trigger in slot

Checklist

Rename

• Delete `elements/pf-v5-popover/`
• 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`)