🔧 Fix invalid email error message

Fix the error message shown in Login and Signup forms when the user
inserts an invalid email address.
With this fix, all frontend tests pass.

Author: you-kimono

frontend/src/routes/login.tsx

@@ -23,7 +23,7 @@ import { PasswordInput } from "@/components/ui/password-input"
 import useAuth, { isLoggedIn } from "@/hooks/useAuth"
 
 const formSchema = z.object({
-  username: z.email(),
+  username: z.email({ message: "Invalid email address" }),
   password: z
     .string()
     .min(1, { message: "Password is required" })

frontend/src/routes/signup.tsx

@@ -22,7 +22,7 @@ import useAuth, { isLoggedIn } from "@/hooks/useAuth"
 
 const formSchema = z
   .object({
-    email: z.email(),
+    email: z.email({ message: "Invalid email address" }),
     full_name: z.string().min(1, { message: "Full Name is required" }),
     password: z
       .string()