[feat]: Update `<pf-v6-text-input>` for PatternFly v6

[bennypowers]

Summary

Update <pf-v6-text-input> to implement the PatternFly v6 Text input component.

Single-line text input with type variants (text, password, email, etc.) and validation states.

Prior Art

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

Notes

• Implement as a Form-Associated Custom Element (FACE) using ElementInternals
• Use ARIA IDL attributes for cross-root ARIA (Baseline 2025)
• Consider referenceTarget for label association (Chrome-only, progressive enhancement)

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with @patternfly/react-core TextInput
• MUST participate in native form submission via FACE
• MAY adjust element API to leverage web platform strengths
• SHOULD maintain CSS custom property theming compatibility
• SHOULD expose useful CSS shadow parts