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

Start with elements/pf-v5-text-area/ and .claude/ADVICE.md, then review the related exports in elements/package.json and references in _snippets/ and framework-integration/. Implement the PFv6 component, demos, and FACE behavior described here, and run the listed API, accessibility, form-submission, lint, and style checks; completion includes a changeset and a staging/pfv6-targeted PR.

Summary

Update `` to implement the PatternFly v6 Text area component.

Multi-line text input with resize options and validation states.

Prior Art

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` TextArea
• 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

Element-specific considerations

• React `validated`: `default`, `success`, `warning`, `error` - same as TextInput; `error` sets `aria-invalid`
• React `resizeOrientation`: `horizontal`, `vertical`, `both`, `none` - CSS `resize` property; map to `resize` attribute
• React `autoResize` - grows textarea height with content; implement via JS (no native equivalent)
• React `rows` - pass through to inner `<textarea>`
• Expose `value`, `placeholder`, `required`, `readonly`, `disabled`, `aria-*` as reflected attributes

Checklist

Rename

• Delete `elements/pf-v5-text-area/`
• Update `elements/package.json` exports
• Update `eslint.config.js` ignore globs if applicable
• Update docs `_snippets/` and `framework-integration/` references

Implementation

• API per `.claude/ADVICE.md`
• CSS uses v6 tokens, logical properties, nesting
• `@summary` and JSDoc on element class
• `formAssociated = true` and `ElementInternals` for form participation
• Form submission tested

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`)