#20159 fix(webviews): align new tab gallery with current props

Changelog

Fixed the legacy New Tab gallery fixture to match the current NewTabPage props after #20127 removed default-kind and harness callbacks.

This clears the feat-cmux-next web typecheck base red introduced by the merged gallery coverage change.

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Summary by cubic

Fixes the legacy New Tab gallery fixture so the feat-cmux-next web typecheck base passes again after #20127 removed the default-kind and harness callback props.

• Drops defaultKind, onSetDefaultKind, and onAddHarness from the fixture and the withReceipt wrapper, along with their recording callbacks.