fix(tag): icon inherits checked text color

[rwv]

Summary

Fixes n-tag checkable checked state: the icon rendered by the #icon slot now follows the checked text color.

Changes

• Make .n-tag__icon inherit color from .n-tag (so --n-text-color-checked applies in checked state).
• Add a regression test for the generated CSS.
• Update the checkable demo (enUS/zhCN) to show an icon on the last tag.
• Add changelog entries.

Related

Closes #7407

Testing

• pnpm test -- src/tag/tests/Tag.spec.ts src/tag/tests/server.spec.tsx
• pnpm dev then toggle the last checkable tag in the Tag demo page.