feat(adminsite): scaffold and site/'s token system

A fifth Next.js app, built like web/ and site/: App Router, React 18,
Tailwind 3, TanStack Query, standalone output.

app/globals.css carries site/app/globals.css's token blocks copied verbatim
rather than retyped, so the two cannot drift by transcription. Tailwind holds
var() references only -- no component or config entry may contain a hex
value. The semantic three are aliased: site/'s --up/--pend/--down become
valid/warn/expired, so each app names the colours for what it shows.

Unlike web/, there is no rewrite proxy: the browser calls admin directly, so
NEXT_PUBLIC_ADMIN_API_URL must be browser-reachable and listed in admin's
ADMIN_ORIGIN.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

adminsite/components/EnvBadge.tsx

@@ -0,0 +1,22 @@
+/*
+ * Sandbox is hatched as well as coloured, so it survives a colourblind reader
+ * and a glance. It sits in the same place on every screen: issuing against the
+ * wrong environment should feel wrong before you click.
+ */
+const ENV = process.env.NEXT_PUBLIC_ADMIN_ENV === "sandbox" ? "sandbox" : "production";
+
+export function EnvBadge() {
+    const sandbox = ENV === "sandbox";
+    return (
+        <span
+            className={
+                sandbox
+                    ? "inline-flex items-center gap-2 rounded-sm border border-warn px-2 py-1 font-mono text-[0.72rem] uppercase tracking-[0.1em] text-ink [background-image:repeating-linear-gradient(-45deg,var(--accent-wash)_0_6px,transparent_6px_12px)]"
+                    : "inline-flex items-center gap-2 rounded-sm bg-accent px-2 py-1 font-mono text-[0.72rem] uppercase tracking-[0.1em] text-accent-ink"
+            }
+        >
+            <i className="h-1.5 w-1.5 shrink-0 rounded-full bg-current" />
+            {sandbox ? "Sandbox" : "Production"}
+        </span>
+    );
+}