feat(ui): add closable Tag support

[wyf027]

Summary

• Add closable, closeIcon, closeAriaLabel, and onClose support to Tag, aligning with mature Tag APIs.
• Support event.preventDefault() in onClose to keep the tag visible for confirmation or controlled removal flows.
• Add first Tag tests and update the VitePress example to use Tailwind layout classes.

Validation

• GitHub Actions CI run 28911208037 passed for commit 6f2b6c84345114c2b773371fe4612ecb49cdf16d.
• CI quality job passed: Install, Lint UI, Typecheck UI, Test UI, Build UI, Build docs.
• Local npm run lint:ui, npm run typecheck:ui, npm run test:ui, and npm run build could not be executed because the local shell runner failed to create a process in this Codex environment.

[ecc-tools]

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