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

[bennypowers]

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

Source	Element	Status
PFE v4	--	--
cem	<pf-v6-text-input-group>	Exists
cockpit	<pf-v6-text-input-group>	Exists
chickadee	--	--

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)