Account impersonation via case-sensitive email uniqueness

Authentication flaw in Lunary before 1.0.2 allows remote attackers to create duplicate identities by changing an email address's letter case. The signup path compares email strings case-sensitively instead of normalizing them before enforcing uniqueness, so differently cased forms of one address receive separate accounts. No authentication or user interaction is required, and the resulting identity collision enables account impersonation and user confusion without interrupting service.