fix(build): include assets in standalone output

With output: "standalone", next build writes server.js under
.next/standalone but leaves generated static/public assets in the
project root, so starting the standalone server directly (e.g. via PM2)
404s on JS/CSS/font/favicon requests and /login stays stuck loading.
Add a postbuild step that copies .next/static and public into the
standalone directory, skipping the workspace-traced CLI build which
already copies its own assets.

package.json

@@ -7,6 +7,8 @@
     "dev": "next dev --port 20127",
     "dev:webpack": "next dev --webpack --port 20127",
     "build": "next build --webpack",
+    "postbuild": "node scripts/copy-standalone-assets.mjs",
+    "postbuild:bun": "node scripts/copy-standalone-assets.mjs",
     "start": "next start --port 20127",
     "dev:bun": "bun --bun next dev --webpack --port 20127",
     "build:bun": "bun --bun next build --webpack",