Filter logs paths to log files

[GreyforgeLabs]

Summary

• Share log-file detection between normal log selection and logs --paths.
• Filter logs --paths output to .log and .txt files instead of every regular file.
• Add CLI regression coverage for ignoring non-log files.

Fixes PlatformNetwork/bounty-challenge#52680.

Validation

• cargo test -p cortex-cli --test logs_paths --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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