Fix: show a widget render failure as an internal error

[SandObserver]

Summary

• In poll(), tag an error thrown after a successful fetch (by render, isEmpty or onEmpty) with kind internal, so the error state reads "Something went wrong" instead of "Out of reach".
• Keep an existing kind on the thrown error, and wrap a frozen or non-object throw in an Error.
• Refresh cache-busting stamps for widget-toolbox.js.

Testing
All green. Added a test that a render failure maps to internal and a fetch failure to network.

Changelog

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.