Include the existing native sharedPhotoShareId in the SharedImage
getSharedImage() result so the web layer can identify the current share.
Add shareId to the native result dictionary and plugin response (NSNull on
the no-image branch), and add shareId: string to the TypeScript
SharedImageResult interface.
This surfaces a value that was already produced natively (previously used
only for logging) so application code can later pass it to markProcessed().
No behavior changes beyond exposing the value; Android untouched. Updates
doc/share-target-ios-audit.md accordingly.
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