Fix Checkbox labels inside Field

[cyphercodes]

Fixes #3876.

Summary

• Omit Label's rendered for attribute when the resolved target is not a labelable HTML element, avoiding Chrome's warning for Field + Label + Checkbox.
• Keep label click/focus behavior by resolving the internal target id even when for is not rendered.
• Use the target's role attribute when forwarding label clicks to ARIA checkbox/radio/switch controls.
• Add a checkbox regression test that verifies no invalid for attribute is rendered, label clicks still toggle/focus the checkbox, and form data is preserved.

Test plan

• CI=true npm run react test checkbox label
• npx tsc -p packages/@headlessui-react/tsconfig.json --noEmit --pretty false
• npx prettier --check packages/@headlessui-react/src/components/label/label.tsx packages/@headlessui-react/src/components/checkbox/checkbox.test.tsx packages/@headlessui-react/src/utils/dom.ts

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