Fix docker.nix to copy hidden .next directory

The glob * doesn't include hidden files/directories. Use /. suffix
to copy all contents including .next from standalone output.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker.nix

@@ -54,10 +54,10 @@ let
       mkdir -p $out
 
       # Copy standalone server (self-contained with minimal node_modules)
-      cp -r .next/standalone/* $out/
+      # Use /. to include hidden directories like .next
+      cp -r .next/standalone/. $out/
 
       # Copy static assets (Next.js standalone requires these separately)
-      mkdir -p $out/.next
       cp -r .next/static $out/.next/static
 
       # Copy public assets