fix(web): make motion animations instant when reduced motion is on

Motion's reducedMotion="user" only drops transforms, so opacity fades
still ran and could be caught half-faded (axe flagged the assistant).
The design makes every duration instant under reduced motion, as the
CSS tokens already do.

apps/web/src/libs/motion.ts

@@ -1,4 +1,5 @@
 import type { CSSProperties } from "react";
+import { MotionGlobalConfig } from "motion/react";
 
 // Motion (JS) mirrors of the CSS motion tokens in packages/ui/src/styles/globals.css (--d1/--d2/--d3, --ease,
 // --ease-in-out-strong). Durations are in seconds, Motion's unit; multiply by 1000 for APIs that take ms (dnd-kit).
@@ -45,3 +46,16 @@ export const stagger = (index: number) => ({ "--stagger": `${Math.min(index, 5)
 
 /** A status icon arriving in place (a success check, a spinner taking its slot): fades and scales up from 90% over D1. */
 export const POP_CLASS = "starting:scale-90 starting:opacity-0 transition-[opacity,scale] duration-quick ease-enter";
+
+/**
+ * Reduced motion makes every duration instant (DESIGN.md, Motion). The CSS tokens drop to 1ms; Motion's own
+ * `reducedMotion="user"` only drops transforms and still fades, so its animations are made instant here as well.
+ */
+export function followReducedMotion() {
+	const query = window.matchMedia("(prefers-reduced-motion: reduce)");
+	const apply = () => {
+		MotionGlobalConfig.instantAnimations = query.matches;
+	};
+	apply();
+	query.addEventListener("change", apply);
+}

apps/web/src/main.tsx

@@ -1,11 +1,14 @@
 import { RouterProvider } from "@tanstack/react-router";
 import ReactDOM from "react-dom/client";
+import { followReducedMotion } from "./libs/motion";
 import { getRouter } from "./router";
 import "./index.css";
 
 const rootElement = document.getElementById("app");
 if (!rootElement) throw new Error("Root element not found");
 
+followReducedMotion();
+
 const router = await getRouter();
 
 // Server metadata describes the initial URL. The SPA router owns these tags after