T1/Phase 1: scaffold Vite SPA + Hono API + Bun worker

- apps/web: Vite + React 19 + TanStack Router/Query + shadcn/ui
   - apps/api: Hono + Bun on :3001 with /api/health, /api/auth/*, /mcp stubs
   - apps/worker: Bun worker stub, DB connection, graceful SIGTERM
   - apps/web-legacy/: old Next.js code moved aside (preserved for T2-T8 reference)
   - Dockerfiles: api (Bun), worker (Bun), spa (multi-stage Caddy)
   - Caddyfile: serves dist + reverse-proxies /api/* + /mcp to api
   - docker-compose.yml: 4-service target (api, spa, db, worker)
   - packages/db/src/client.ts: shared Drizzle client for api + worker
   - db/client.ts: root-level alias for convenience

   Parent: t_e1cbd87d -> t_24c9c3fd (T0)

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

@@ -0,0 +1,32 @@
+import Link from 'next/link';
+import { Button } from '@/components/ui/button';
+import {
+  Card,
+  CardContent,
+  CardFooter,
+  CardHeader,
+  CardTitle,
+} from '@/components/ui/card';
+
+export default function NotFound() {
+  return (
+    <div className="flex min-h-[50vh] items-center justify-center p-6">
+      <Card className="max-w-md w-full">
+        <CardHeader>
+          <CardTitle>Page not found</CardTitle>
+        </CardHeader>
+        <CardContent>
+          <p className="text-muted-foreground">
+            The page you&apos;re looking for doesn&apos;t exist or has been
+            moved.
+          </p>
+        </CardContent>
+        <CardFooter>
+          <Button asChild>
+            <Link href="/">Go home</Link>
+          </Button>
+        </CardFooter>
+      </Card>
+    </div>
+  );
+}