feat(aura): add Carbon Blue atmospheric background partial

styles/base/global.css

@@ -83,3 +83,44 @@ main#maincontent {
 /* Responsive embeds */
 .embed { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; }
 .embed iframe, .embed object, .embed embed, .embed video { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }
+
+/* Carbon Blue atmospheric field (decorative — content must sit in z-index: 1) */
+.aura-bg {
+	position: relative;
+	overflow: hidden;
+	min-height: 100vh;
+	isolation: isolate;
+}
+
+.aura-layer-1 {
+	position: absolute;
+	inset: 0;
+	background: linear-gradient(138deg, #05070c 0%, #0f172a 40%, #172554 70%, #1e3a8a 100%);
+	mix-blend-mode: normal;
+	pointer-events: none;
+	transform: translateZ(0);
+	will-change: transform;
+}
+
+.aura-layer-2 {
+	position: absolute;
+	inset: 0;
+	background: radial-gradient(ellipse 45% 50% at 72% 40%, rgba(96, 165, 250, 0.20) 0%, transparent 68%);
+	mix-blend-mode: screen;
+	pointer-events: none;
+	transform: translateZ(0);
+	will-change: transform;
+}
+
+.aura-layer-2--mobile { filter: blur(105px); }
+.aura-layer-2--desktop { filter: blur(151px); }
+
+.aura-grain {
+	position: absolute;
+	inset: 0;
+	mix-blend-mode: overlay;
+	opacity: 0.85;
+	pointer-events: none;
+}
+
+.aura-grain svg { display: block; width: 100%; height: 100%; }