Unauthenticated account enumeration via distinct login errors

Observable response discrepancy in Shopware allows remote attackers to enumerate customer accounts through the Store API login endpoint. LoginRoute lets CustomerNotFoundException propagate to ErrorResponseFactory, which serializes a distinct code and echoes the probed email instead of normalizing it to the bad-credentials response. No authentication is required; a single probe per candidate address reveals account existence, although per-email and per-IP rate limiting slows bulk enumeration.