fix: align help paths with cortex home

[Bortlesboat]

Summary

• update root help PATHS examples to use the canonical ~/.cortex home layout
• document CORTEX_HOME as overriding Cortex home instead of ~/.config/cortex
• add an integration regression test for the root --help output

Verification

• cargo test -p cortex-cli --test help_paths -- --nocapture
• cargo check -p cortex-cli
• cargo fmt --check --package cortex-cli
• git -c safe.directory=C:/Users/andre/projects/bittensor-subnets/cortex-pr-49248 diff --check

[greptile-apps]

Your free trial has ended. If you'd like to continue receiving code reviews, you can add a payment method here.