feat: replace calc topbar controls with popup menus

samples/calc-01/index.css

@@ -167,8 +167,11 @@ body {
   box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.05);
 }
 
-.topbar-label,
-.mode-select > span {
+.menu-cell {
+  position: relative;
+}
+
+.topbar-label {
   display: block;
   margin-bottom: 6px;
   font-size: 11px;
@@ -193,21 +196,41 @@ body {
   background: rgba(255, 255, 255, 0.06);
 }
 
-.mode-select {
-  display: grid;
-  gap: 6px;
-  min-width: 0;
-  font-size: 12px;
-}
-
-.mode-cell select {
+.menu-trigger {
   width: 100%;
+  min-height: 38px;
 }
 
-.const-buttons {
+.popup-menu {
+  position: absolute;
+  top: calc(100% + 8px);
+  left: 10px;
+  right: 10px;
+  z-index: 20;
   display: grid;
-  grid-template-columns: repeat(2, minmax(0, 1fr));
   gap: 8px;
+  padding: 10px;
+  border-radius: 14px;
+  background: rgba(18, 24, 34, 0.96);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  box-shadow: 0 16px 30px rgba(0, 0, 0, 0.35);
+}
+
+.popup-menu[hidden] {
+  display: none;
+}
+
+.popup-menu-compact {
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+}
+
+.hidden-select {
+  position: absolute;
+  left: -9999px;
+  width: 1px;
+  height: 1px;
+  opacity: 0;
+  pointer-events: none;
 }
 
 .action-cell {
@@ -215,8 +238,7 @@ body {
   align-items: stretch;
 }
 
-.action-cell > button,
-.const-buttons > button {
+.action-cell > button {
   width: 100%;
 }