fix: native preview should decode (#2631)

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## Summary by CodeRabbit

* **Bug Fixes**
* Properly decode multi-encoded URL parameters in initialization data
before use.

* **Changes**
* Preview/share URLs now embed payloads or use a demo ID directly in the
query string (messages, action mocks, speed, theme) instead of using an
external shortening step.

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## Checklist

<!--- Check and mark with an "x" -->

- [ ] Tests updated (or not required).
- [ ] Documentation updated (or not required).
- [ ] Changeset added, and when a BREAKING CHANGE occurs, it needs to be
clearly marked (or not required).