fix(ui): describe radio helper and error text

[wyf027]

Summary

• add optional helperText and error feedback props to Radio
• associate Radio helper/error text with the native radio input via aria-describedby
• set aria-invalid automatically when Radio renders an error
• preserve consumer-provided aria-describedby and append internal helper/error descriptions
• add focused tests and document Radio accessibility behavior

Validation

• GitHub Actions CI / quality succeeded for head 650215413ca26096923b3cd3d64be73b0e3597f4.
  • Install
  • Lint UI
  • Typecheck UI
  • Test UI
  • Build UI
  • Build docs
• Not run locally: the Codex shell executor is currently failing with Failed to create unified exec process: No such file or directory.

Notes

• codebase-memory-mcp graph tools were not exposed in this session, so this run used repository files through GitHub as the AGENTS.md fallback.
• PR fix(ui): describe checkbox helper and error text #68 is still open and mergeable, so this branch intentionally targets Radio from the current main and does not touch Checkbox files.

[ecc-tools]

ECC bundle files are already tracked in this repository. Skipping generation of another bundle PR.