Add .dockerignore to avoid docker building error

[Robert-Jia00129]

Simple thing to add, I'll add this after Christmas.

add node_modules/ to .dockerignore file to avoid the following error when trying to build and download the image locally langgraph build -t open-canvas instead of pulling every time with langgraph up --watch --port 54367

#4 [internal] load build context
#4 transferring context: 563.45MB 4.3s
#4 transferring context: 845.89MB 9.3s
#4 transferring context: 966.14MB 11.1s done
#4 CANCELED
ERROR: failed to solve: error from sender: context canceled
#4 transferring context: 966.14MB 11.1s done
#4 CANCELED