fix: add import fallbacks for missing optional tokens (v1.2.3)

[kkugot]

Summary

Make import-export.sh more tolerant of incomplete theme files by filling the two commonly omitted optional tokens during import.

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Context / Motivation

Users can have valid theme files that omit selectedListItemText or backgroundMenu, but the import flow previously treated those gaps as hard failures instead of following the same fallback behavior used by the app.

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Changes

• add import-time fallbacks for selectedListItemText -> background
• add import-time fallbacks for backgroundMenu -> backgroundElement
• preserve existing color, defs, and single-mode import handling while producing clearer missing-token errors for truly required fields
• bump the package version to 1.2.3

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Testing

• ✅ npm run test
• ✅ npm run lint
• ✅ npm run build
• ✅ verified public/import-export.sh with the provided incomplete theme JSON

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Version

Patch release: 1.2.3