init: arcadia-admin — admin webapp for arcadia-core, cloned from vibespace

Initial commit. Spun up via the docs/STARTER.md recipe: cp from vibespace,
reset git, rename package, set brand to "Arcadia Admin" with Shield icon
in app/lib/identity.ts.

Inherits the full Crema sibling-lib wiring including @crema/arcadia-client
(typed HTTP + Phoenix Channels realtime against arcadia-core) and
@crema/arcadia-auth-ui (login/signup/password-reset/2FA forms). The /login
route already renders <LoginForm>; <ArcadiaProvider> in app/root.tsx reads
VITE_ARCADIA_URL (default localhost:4000) and VITE_ARCADIA_TENANT (default
"default").

CLAUDE.md and README rewritten to frame this as the admin app for
arcadia-core. docs/STARTER.md removed — arcadia-admin is a leaf consumer,
not a downstream starter.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/components/layout/theme-toggle.tsx

@@ -0,0 +1,30 @@
+import { Moon, Sun } from "lucide-react"
+
+import { Button } from "~/components/ui/button"
+
+const STORAGE_KEY = "crema-theme"
+
+function applyTheme(next: "light" | "dark") {
+  document.documentElement.classList.toggle("dark", next === "dark")
+  localStorage.setItem(STORAGE_KEY, next)
+}
+
+export function ThemeToggle() {
+  const toggle = () => {
+    const isDark = document.documentElement.classList.contains("dark")
+    applyTheme(isDark ? "light" : "dark")
+  }
+
+  return (
+    <Button
+      data-action="theme-toggle"
+      variant="ghost"
+      size="icon-sm"
+      aria-label="Toggle theme"
+      onClick={toggle}
+    >
+      <Sun className="hidden dark:block" />
+      <Moon className="block dark:hidden" />
+    </Button>
+  )
+}