[feat]: Create `<pf-v6-drawer>` element

[bennypowers]

Summary

Create `` to implement the PatternFly v6 Drawer component.

Slide-out panel overlay or inline panel for secondary content, details, or actions.

Prior Art

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

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Drawer
• 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 `isExpanded` / `defaultExpanded` - open/close state; map to `expanded` attribute; emit `toggle` event
• React `isInline` - panel is inline (pushes content) vs overlay (overlaps); map to `inline` attribute
• React `isStatic` - always visible, no toggle; map to `static` attribute
• React `position`: `right`, `left`, `bottom` - map to `position` attribute
• React `onExpand` - called after animation ends; emit `expanded` event
• React sub-components: `DrawerContent`, `DrawerContentBody`, `DrawerPanelContent`, `DrawerPanelBody`, `DrawerHead`, `DrawerActions`, `DrawerCloseButton` - use named slots
• Panel width/height as CSS custom property (default ~50%)
• Responsive: panel may become full-width on mobile
• Focus management: when drawer opens, focus should move into the panel; on close, return to trigger

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

Reviews

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

Ship

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