fix(infra): ship next.config.ts into Nix store for hub

next start re-reads next.config.ts at runtime; the OLD store had only
.next/public/package.json/node_modules, so images.maximumDiskCacheSize
fell back to defaults (undefined) and the image-optimizer disk LRU did
mkdir(<store>/.next/cache/images) -> EACCES on every optimized image.
Also now that next.config.ts sets maximumDiskCacheSize:0 +
isrFlushToDisk:false, shipping the file makes runtime match the baked
build config, eliminating the EACCES spike.

flake.nix

@@ -88,6 +88,7 @@
             cp -r .next $out/share/hub/
             cp -r public $out/share/hub/ 2>/dev/null || true
             cp package.json $out/share/hub/
+            cp next.config.{ts,mjs,js} $out/share/hub/ 2>/dev/null || true
             cp -r node_modules $out/share/hub/
             cat > $out/bin/hub << WRAPPER
 #!${pkgs.runtimeShell}