Respect level filter when clearing logs

[GreyforgeLabs]

Summary

• Honor --level when logs --clear selects files for deletion.
• Preserve non-matching level log files during level-scoped cleanup.
• Add CLI regression coverage for logs --clear --level error keeping debug/info logs.

Fixes PlatformNetwork/bounty-challenge#51573.

Validation

• cargo test -p cortex-cli --test logs_clear_level --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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