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

Read .claude/ADVICE.md, then compare the PatternFly Toolbar documentation with the existing cem and cockpit implementations. Identify the repository entry points for the toolbar, item and group subcomponents, demos, and tests. Done means the v6 visual and API requirements, accessibility snapshots, lint/review checks, changeset, and staging/pfv6 target are satisfied.

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

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`)