Packaging & deployment improvements (uv python package, dockerization)

[lee-b]

These are some small changes to make this easier to run via docker, or to deploy via docker compose. They:

• Add docker and docker compose support
• Add READER3_HOST and READER3_PORT env vars, with unchanged defaults
• Move both python scripts into a reader3 python package
• Create two executable script wrappers reader3-server, which is just a more clearly named and... well, executable... executable for what server.py used to do; reader3ctl, which is basically just what running reader.py used to do, but takes an instruction, add: reader3ctl add data/dracula.pub.
• Update the code to handle BOOKS_DIR better, allowing data/ as a prefix for all of the books.
• Update README accordingly.