fix: case-insensitive email matching in auth and password reset

Email lookups used findUnique (case-sensitive on PostgreSQL) but user
input was lowercased, causing login failures for users with mixed-case
emails stored in the DB (e.g. Laurent_Faure@dietsmann.com). Also
normalized 7 affected emails to lowercase on the production DB.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app/api/auth/check-email/route.ts

@@ -24,8 +24,8 @@ export async function POST(req: NextRequest) {
       return NextResponse.json({ exists: false }, { status: 400 })
     }
 
-    const user = await prisma.user.findUnique({
-      where: { email: email.toLowerCase().trim() },
+    const user = await prisma.user.findFirst({
+      where: { email: { equals: email.toLowerCase().trim(), mode: 'insensitive' } },
       select: { status: true },
     })