Import source: src/components/shell/ambient-background

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

src/components/shell/ambient-background.tsx

@@ -0,0 +1,16 @@
+/**
+ * Fixed full-viewport ambient layer rendered behind the app shell:
+ * slow-drifting aurora blobs tinted by the active accent, a fading
+ * grid, and a film-grain overlay. Disabled via data-ambiance="off".
+ */
+export function AmbientBackground() {
+  return (
+    <div aria-hidden className="pointer-events-none fixed inset-0 -z-10 overflow-hidden">
+      <div className="ambient-grid" />
+      <div className="aurora aurora-1" />
+      <div className="aurora aurora-2" />
+      <div className="aurora aurora-3" />
+      <div className="grain" />
+    </div>
+  );
+}