Add CLI integration tests for all public commands

[SinghCod3r]

Add integration tests for all documented CLI commands:

build
validate
eval
improve
compare
report

Cover:

• --help
• valid invocation
• missing arguments
• invalid paths
• invalid configuration
• expected non-zero exits
• JSON output where supported

Tests must not require a paid external API.

[SinghCod3r]

Hey, @johndavidagaba , Would you like to work on this issue ? . If yes do tag me here so that I can assign this issue to you.