fix: ensure immediate visibility for initial mount in useMotion

Author: tanerengiiin

packages/@primereact/core/src/motion/useMotion.ts

@@ -100,6 +100,15 @@ export const useMotion = withHeadless({
             if (props.visible) {
                 if (shouldAppear || !isInitialMount.current) {
                     enter?.();
+                } else if (props.cssVarPrefix) {
+                    // Initial mount with visible=true and no appear animation.
+                    // createMotion sets CSS vars to 0px, so we need to override them to auto
+                    // to ensure the content is visible immediately.
+                    const widthVar = resolveCSSVarName(props.cssVarPrefix, 'width');
+                    const heightVar = resolveCSSVarName(props.cssVarPrefix, 'height');
+
+                    element.style.setProperty(widthVar, 'auto');
+                    element.style.setProperty(heightVar, 'auto');
                 }
             } else {
                 leave?.()?.then(() => {