feat(calc-02): add shared popup menus for mode and constants

Refactor the calc-02 demo to use a single popup menu component for angle mode and constants, align the menus to their trigger buttons, and update the README/project notes to reflect the portrait-first demo layout and constant API.

samples/calc-02/index.css

@@ -1,5 +1,4 @@
 
-
 :root {
 	--bg0: #10151e;
 	--bg1: #1b2432;
@@ -42,7 +41,6 @@ body {
 	background: var(--bg0);
 }
 
-
 .app-shell {
 	min-height: 100vh;
 	display: grid;
@@ -113,9 +111,6 @@ body {
 	max-height: 138px;
 	margin-bottom: 0;
 }
-
-
-
 .display-grid {
 	height: 100%;
 	display: grid;
@@ -125,7 +120,6 @@ body {
 	gap: 2px;
 }
 
-
 .stack-cell {
 	display: grid;
 	grid-template-columns: 2.2ch auto minmax(0, 1fr);
@@ -137,7 +131,6 @@ body {
 	padding-block: 0;
 }
 
-
 .stack-label {
 	text-align: right;
 	opacity: 0.78;
@@ -152,8 +145,6 @@ body {
 	justify-self: end;
 	font-size: 20px;
 }
-
-
 .display-buttons-panel {
 	grid-area: display-buttons;
 	padding: 8px;
@@ -183,7 +174,6 @@ body {
 	box-shadow: none;
 }
 
-
 .display-button-symbol {
 	display: inline-flex;
 	align-items: center;
@@ -203,8 +193,7 @@ body {
 	padding: 6px 8px;
 }
 
-
-.mode-menu {
+.menu-popup {
 	position: fixed;
 	z-index: 20;
 	display: flex;
@@ -218,7 +207,7 @@ body {
 	backdrop-filter: blur(2px);
 }
 
-.mode-menu-item {
+.menu-popup-item {
 	width: 100%;
 	min-width: 0;
 	padding: 6px 10px;
@@ -228,7 +217,7 @@ body {
 	font-weight: 700;
 }
 
-.mode-menu-item.is-active {
+.menu-popup-item.is-active {
 	outline: 1px solid rgba(207, 224, 174, 0.7);
 	outline-offset: 0;
 }
@@ -295,10 +284,6 @@ body {
 .functions-grid,
 .trigo-grid {
 	grid-template-columns: repeat(4, minmax(0, 1fr));
-}
-
-.functions-grid,
-.trigo-grid {
 	grid-template-rows: repeat(2, minmax(0, 1fr));
 }
 
@@ -321,7 +306,6 @@ button:hover {
 	filter: brightness(1.06);
 }
 
-
 button:active {
 	transform: none;
 	box-shadow: none;
@@ -342,8 +326,6 @@ button:active {
 		opacity: 0.7;
 	}
 }
-
-
 .stack-copy-button {
 	padding: 4px;
 	min-width: 24px;