Show initial lines before following logs

[GreyforgeLabs]

Summary

• Print the requested initial tail window before entering logs --follow mode.
• Apply the existing --level filter to the initial follow output as well as new lines.
• Add a CLI regression test that confirms logs --follow --lines 2 emits the last two existing lines before tailing.

Fixes PlatformNetwork/bounty-challenge#51529.

Validation

• cargo test -p cortex-cli --test logs_follow_lines --no-default-features --features cortex-tui -- --nocapture
• cargo check -p cortex-cli --no-default-features --features cortex-tui
• cargo fmt --package cortex-cli --check
• git diff --check
• git diff --cached --check

[greptile-apps]

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