Feature: auto-update Dockerfile with the current claude-code npm package version

The Dockerfile now contains the line:

RUN npm install -g @anthropic-ai/claude-code

This should read

RUN npm install -g @anthropic-ai/claude-code@0.2.52

Otherwise if one builds a docker image and wants to subsequently update it to later claude-code versions by rebuilding, the cached layer is being used and claude-code never gets updated.

This is related to #425 and is perhaps a better solution to that problem.