chore: scaffold monorepo and migrate uhd_web design system (W0-A)

- pnpm workspace: apps/{web,server}, packages/{contracts,db,domain,adapters,tasks,agent,testkit}
- server: Hono + zod-openapi, API Key auth with scopes, redacting pino logger, SSE event bus with replay, worker heartbeat
- db: Kysely + pg, file migrator, 0001_init (settings/api_key/audit_event/outbox_event)
- web: React Router 7 SPA console shell with 12 workspace placeholders, uhd_web tokens/ui/guard scripts
- docs: ADR-001 (Node over Deno), dev runbook, design system rules

Co-Authored-By: Claude Fable 5.1 <[email protected]>

apps/web/app/routes/not-found.tsx

@@ -0,0 +1,19 @@
+import { Link } from "react-router";
+import { EmptyState } from "~/components/console/empty-state";
+import { buttonVariants } from "~/components/ui/button";
+
+export default function NotFound() {
+  return (
+    <div className="grid min-h-screen place-items-center bg-background px-4">
+      <EmptyState
+        title="页面不存在"
+        description="检查地址是否正确，或回到首页。"
+        action={
+          <Link to="/" className={buttonVariants({ variant: "outline" })}>
+            回到首页
+          </Link>
+        }
+      />
+    </div>
+  );
+}