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

[bennypowers]

Summary

Create `` to implement the PatternFly v6 Toolbar component.

Horizontal bar for actions, filters, and pagination controls, typically placed above a data view.

Prior Art

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

Sub-components

• `` - Individual toolbar item
• `` - Grouped toolbar items

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Toolbar
• 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 `id` - required for filter chip/label group wiring
• React `clearAllFilters` callback - emit `clear-all-filters` event
• React `collapseListedFiltersBreakpoint` - responsive breakpoint for collapsing filters
• React `inset`, `usePageInsets` - spacing tokens
• React `ToolbarContent` - wraps all items; handles filter chip row
• React `ToolbarGroup`: `variant` (`action-group`, `button-group`, `filter-group`, `icon-button-group`, `label-group`)
• React `ToolbarItem`: `variant`, `visibility`, `alignment`, `spacer`
• React `ToolbarFilter` - wraps a filter control; manages active filter chips/labels (v6: Labels, not Chips)
• React `ToolbarToggleGroup` - collapses filter controls behind a toggle at breakpoints
• v6 change: Filter indicators use `` not Chip - no more chip groups in toolbar

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`)