feat: basic belief node with the basic belief types defined in KB.

ref: N25B-408

src/App.css

@@ -248,3 +248,11 @@ button.no-button {
     text-decoration: underline;
   }
 }
+
+.flex-center-x {
+  display: flex;
+  justify-content: center; /* horizontal centering */
+  text-align: center;       /* center multi-line text */
+  width: 100%;              /* allow it to stretch */
+  flex-wrap: wrap;          /* optional: let text wrap naturally */
+}