fix: make user validation consistent between pages

backend/internal/dto/user_dto.go

@@ -13,7 +13,7 @@ type UserDto struct {
 }
 
 type UserCreateDto struct {
-	Username  string `json:"username" binding:"required,username,min=3,max=20"`
+	Username  string `json:"username" binding:"required,username,min=2,max=50"`
 	Email     string `json:"email" binding:"required,email"`
 	FirstName string `json:"firstName" binding:"required,min=1,max=50"`
 	LastName  string `json:"lastName" binding:"required,min=1,max=50"`

frontend/src/routes/settings/account/account-form.svelte

@@ -16,9 +16,16 @@
 	let isLoading = $state(false);
 
 	const formSchema = z.object({
-		firstName: z.string().min(2).max(50),
-		lastName: z.string().min(2).max(50),
-		username: z.string().min(2).max(50),
+		firstName: z.string().min(1).max(50),
+		lastName: z.string().min(1).max(50),
+		username: z
+			.string()
+			.min(2)
+			.max(30)
+			.regex(
+				/^[a-z0-9_@.-]+$/,
+				"Username can only contain lowercase letters, numbers, underscores, dots, hyphens, and '@' symbols"
+			),
 		email: z.string().email(),
 		isAdmin: z.boolean()
 	});