feat(calc-02): replace display button labels with symbols

samples/calc-02/index.js

@@ -5,9 +5,9 @@ const modeButton = document.getElementById('modeButton');
 const pasteButton = document.getElementById('pasteButton');
 const upButton = document.getElementById('upButton');
 const constButton = document.getElementById('constButton');
-const rightButton = document.getElementById('rightButton');
+const leftButton = document.getElementById('leftButton');
 const downButton = document.getElementById('downButton');
-const constRightButton = document.getElementById('constRightButton');
+const rightButton = document.getElementById('rightButton');
 
 const stackEls = {
 	T: document.getElementById('stackT'),
@@ -289,11 +289,11 @@ upButton.addEventListener('click', () => {});
 
 constButton.addEventListener('click', () => {});
 
-rightButton.addEventListener('click', () => {});
+leftButton.addEventListener('click', () => {});
 
 downButton.addEventListener('click', () => {});
 
-constRightButton.addEventListener('click', () => {});
+rightButton.addEventListener('click', () => {});
 
 window.addEventListener('keydown', handleKeyboard);
 window.addEventListener('load', focusInput);