feat(frontend): safe-area insets + hardened reduced-motion

- Add viewport export with viewportFit: "cover" so iOS exposes
  env(safe-area-inset-*) (required for the insets to take effect).
- NavRail / TopBar / main / Toaster now respect safe-area insets so content
  clears the iPhone notch and home indicator in both portrait and landscape.
- prefers-reduced-motion: the media query already disabled declared animation
  classes; harden it with a global transition/animation duration override and
  kill the scan-line shimmer so motion-sensitive users get a fully static UI.

Verified tsc --noEmit + next build clean.

services/frontend/src/components/shell/ambient-app.tsx

@@ -12,7 +12,7 @@ export function AppFrame({ children }: { children: React.ReactNode }) {
       <NavRail />
       <div className="flex min-w-0 flex-1 flex-col">
         <TopBar />
-        <main className="min-h-0 flex-1 overflow-y-auto px-4 pb-8 sm:px-5">
+        <main className="min-h-0 flex-1 overflow-y-auto px-4 pb-[calc(2rem+env(safe-area-inset-bottom))] sm:px-5">
           {children}
         </main>
       </div>