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/primitives/toast.tsx

@@ -57,7 +57,7 @@ export function Toaster({ position = "bottom-right" }: { position?: string }) {
 
   const pos =
     position === "bottom-right"
-      ? "bottom-4 right-4"
+      ? "bottom-[calc(1rem+env(safe-area-inset-bottom))] right-[calc(1rem+env(safe-area-inset-right))]"
       : position === "top-right"
         ? "top-4 right-4"
         : "bottom-4 left-1/2 -translate-x-1/2";

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>

services/frontend/src/components/shell/nav-rail.tsx

@@ -40,7 +40,7 @@ export function NavRail() {
   const path = pathname ?? "/";
 
   return (
-    <nav className="glass m-3 mr-0 flex w-[68px] flex-col items-center gap-1 rounded-[18px] py-4">
+    <nav className="glass mb-[calc(0.75rem+env(safe-area-inset-bottom))] ml-[calc(0.75rem+env(safe-area-inset-left))] mt-[calc(0.75rem+env(safe-area-inset-top))] flex w-[68px] flex-col items-center gap-1 rounded-[18px] py-4">
       <div className="flex flex-1 flex-col gap-1">
         {navItems.map((item) => (
           <NavItem

services/frontend/src/components/shell/topbar.tsx

@@ -32,7 +32,7 @@ export function TopBar() {
         : "text-signal";
 
   return (
-    <header className="sticky top-0 z-40 flex items-center gap-3 px-4 py-3 sm:gap-4 sm:px-5 sm:py-3.5">
+    <header className="sticky top-0 z-40 flex items-center gap-3 px-4 py-3 pt-[calc(0.75rem+env(safe-area-inset-top))] sm:gap-4 sm:px-5 sm:py-3.5">
       <div className="flex min-w-0 items-baseline gap-2 sm:gap-3">
         <span className="eyebrow hidden sm:inline">GMW</span>
         <h1 className="display truncate text-[1.25rem] text-ink sm:text-[1.5rem]">{label}</h1>