feat(pie-switch): DSW-4019 bind the checked prop correctly and add missing form behaviours

[raoufswe]

Describe your changes (can list changeset entries if preferable)

• [Added] - Wrapped the checked value with the lit live directive to ensure the DOM and component state stay in sync.
• [Added] - Missing defaultChecked prop and form rest logic
• [Changed] - Refactored the toggle between leading and trailing labels to be handled via CSS.
• [Changed] - Updated the component to use a <div> as the parent wrapper when the label prop isn’t provided. This avoids nested <label> elements when consumers wrap the component with an external label, which is an invalid HTML pattern

Author Checklist (complete before requesting a review, do not delete any)

• I have performed a self-review of my code.
• I have added thorough tests where applicable (unit / component / visual).
• I have reviewed the PIE Storybook/PIE Docs PR preview.
• [-] I have reviewed visual test updates properly before approving.
• If changes will affect consumers of the package, I have created a changeset entry.
• If a changeset file has been created, I have tested these changes in PIE Aperture using the /test-aperture command.

Not-applicable Checklist items

Please move any Author checklist items that do not apply to this pull request here.

---

Reviewer checklists (complete before approving)

Mark items as [-] N/A if not applicable.

Reviewer 1

• I have reviewed the PIE Storybook/PIE Docs PR preview.
• I have verified that all acceptance criteria for this ticket have been completed.
• I have reviewed the Aperture changes (if added)
• If there are visual test updates, I have reviewed them.

Reviewer 2

• I have reviewed the PIE Storybook/PIE Docs PR preview.
• I have verified that all acceptance criteria for this ticket have been completed.
• I have reviewed the Aperture changes (if added)
• If there are visual test updates, I have reviewed them.

[pie-design-system-app]

	Fails
🚫	You have unchecked checklist items outside the "Not-applicable Checklist items" section. Please ensure all unchecked checkboxes are moved to the appropriate section.
🚫	You have unchecked checklist items in Reviewer 1's section. Please ensure all items are addressed before approval.
🚫	You have unchecked checklist items in Reviewer 2's section. Please ensure all items are addressed before approval.

Generated by 🚫 dangerJS against 8b49a03

[raoufswe]

/snapit

[pie-design-system-app]

Starting a new snapshot build. You can view the logs here.

[pie-design-system-app]

@raoufswe Your snapshots have been published to npm!

Test the snapshots by updating your package.json with the newly-published versions:

Note

If you have more than one of these packages installed, we suggest using the new snapshots for all of them to help avoid version conflicts.

yarn up @justeattakeaway/pie-cookie-banner@0.0.0-snapshot-release-20260626172928 --mode=update-lockfile

yarn up @justeattakeaway/pie-switch@0.0.0-snapshot-release-20260626172928 --mode=update-lockfile

yarn up @justeattakeaway/pie-webc@0.0.0-snapshot-release-20260626172928 --mode=update-lockfile

Then finally:

yarn install