Load and export .env variables from the mounted directory

[Copilot]

If the mounted directory contains a .env, cli50 now sources it before launching the container and exports the resulting variables into docker run. This lets project-local environment configuration flow into the container without requiring explicit --env flags.

• Behavior

  • Detect <mounted-directory>/.env during container startup.
  • Source it in a clean shell environment.
  • Forward variables introduced or changed by that file as --env entries to the container.
  • Exit early if the .env exists but cannot be sourced.

• Implementation

  • Add env_options(directory) in cli50/__main__.py.
  • Capture a baseline environment, source .env, then diff the result to avoid forwarding shell-added defaults like PWD or SHLVL.
  • Append the resulting --env KEY=VALUE pairs to the existing Docker run options.

• Coverage

  • Add focused tests for:
    • no .env present
    • .env with standard assignments and quoted/exported values

# <mounted-directory>/.env
FOO=bar
export BAZ="qux quux"

This now results in the container receiving:

--env FOO=bar --env BAZ="qux quux"

• Fixes Add support for .env file #123

[dmalan]

Add comments to your blocks of code. Omit test file for now.

[Copilot]

Add comments to your blocks of code. Omit test file for now.

Addressed in ca00d09: added inline comments to the new .env blocks in cli50/__main__.py and removed the test file.