[feat]: Create `<pf-v6-text-input-group>` element

Start with .claude/ADVICE.md and the PatternFly v6 Text input group reference, then review the existing cem and cockpit implementations named in the issue. Implement the component, demos, and tests covering the public API, accessibility snapshot, and form submission. Done means the checklist passes, including visual parity, review commands, linting, and a changeset targeting staging/pfv6.

Summary

Create a <pf-v6-text-input-group> web component implementing the PatternFly v6 Text input group component.

Composed text input with utilities like search icon, clear button, and chip display for filter/tag inputs.

Prior Art

Requirements

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

• isDisabled / isPlain props on wrapper
• TextInputGroupMain: contains the actual <input>; props: icon, hint, type, value, onChange, aria-label
• TextInputGroupUtilities: slot for labels/chips shown after the input (e.g. selected filter tags), plus clear button
• Input is FACE - use formAssociated = true and ElementInternals for form participation
• Used as base for multi-select typeahead and chip-group filter patterns
• In v6, filter indicators use pf-v6-label not chips (Label replaced Chip)
• Hint text renders inside input as ghost/placeholder-style text
• Icon slot or icon attribute for leading icon (search, filter, etc.)

Checklist

Implementation

• formAssociated = true
• ElementInternals for value/validity reporting
• 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
• Form submission test

Reviews

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

Ship

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