Match log levels exactly

[GreyforgeLabs]

Summary

• Parse log lines for recognized level tokens instead of searching full message text.
• Use exact log-level comparison for logs --level and follow-mode filtering.
• Add CLI regression coverage for message text false positives and partial level names.

Fixes PlatformNetwork/bounty-challenge#51536.

Validation

• cargo test -p cortex-cli --test logs_level_filter --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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