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

[bennypowers]

Summary

Update `` to implement the PatternFly v6 Modal component.

Dialog overlay for focused tasks, confirmations, or information display. Supports size variants and custom footers.

Prior Art

Source	Element	Status
PFE v4	``	Exists
cem	``	Exists
cockpit	``	Exists
chickadee	``	Exists

Notes

• Should use the native `` element internally
• Use `popover` attribute where appropriate for light-dismiss behavior

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Modal
• 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 `variant`: `small`, `medium`, `large`, `xlarge`, `default` - map to `size` attribute
• React `isScrollable` - scrollable body with sticky header/footer; map to `scrollable` attribute
• React `title`, `titleIconVariant` (`success`, `danger`, `warning`, `info`, `custom`) - use slot or attribute
• React `actions` - footer button group; use `slot="footer"`
• React `description` - subtitle below title
• React `hasNoBodyWrapper` - removes the default `ModalBoxBody` padding wrapper
• React `disableFocusTrap` - should almost never be needed; do not expose unless truly necessary
• Native `` handles: focus trap, Escape key close, backdrop (`::backdrop` pseudo-element)
• Light-dismiss (click outside): use `dialog.addEventListener("click", ...)` pattern on backdrop
• `showModal()` vs `show()` vs `popover`: use `showModal()` for proper modal semantics (blocks interaction)
• Expose `open` property/attribute for declarative open/close

Checklist

Rename

• Delete `elements/pf-v5-modal/`
• 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`)