fix: update button size handling in CTA component

- Changed the size prop for the CTA button to use "custom" instead of undefined for better consistency.
- Added "custom" variant to button styles for improved flexibility.

packages/survey-ui/src/components/elements/cta.tsx

@@ -95,7 +95,7 @@ function CTA({
               disabled={disabled}
               className="text-button font-button-weight flex items-center gap-2"
               variant={buttonVariant}
-              size={buttonVariant === "custom" ? null : undefined}>
+              size={"custom"}>
               {buttonLabel}
               <SquareArrowOutUpRightIcon className="size-4" />
             </Button>

packages/survey-ui/src/components/general/button.tsx

@@ -23,6 +23,7 @@ const buttonVariants = cva(
         sm: "h-8 rounded-md gap-1.5 px-3 has-[>svg]:px-2.5",
         lg: "h-10 rounded-md px-6 has-[>svg]:px-4",
         icon: "size-9",
+        custom: "",
       },
     },
     defaultVariants: {