Add SharedImageUtility.clearProcessedShare() to permanently delete the
shared image file and remove all App Group metadata (sharedPhotoFileName,
sharedPhotoFilePath, sharedPhotoShareId, sharedPhotoReady,
sharedPhotoProcessedShareId). The helper is idempotent and logs cleanup
started/completed plus a warning on file-deletion failure. Expose it through
the SharedImage plugin with a web no-op stub.
Wire cleanup into the import flow so it runs only after both
storeSharedImageInTempDB() and markProcessed() succeed; a cleanup failure is
logged but does not fail the already-successful import. After cleanup a
subsequent getSharedImage() finds no pending share. iOS only; Android, the
Share Extension, and Phase 1E duplicate suppression are unchanged.
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