Add unit tests for the diagnose CLI command

[himanshu231204]

Description

The \oaeval diagnose\ command (failure diagnosis) has limited test coverage. Adding unit tests for the CLI layer would improve reliability.

What to Test

• Command argument parsing
• Integration with the diagnosis module
• Report output in different formats
• Edge cases (no failures, all failures, mixed results)

Files to Look At

• \openagent_eval/cli/commands/diagnose.py\ — the command implementation
• \ ests/unit/test_diagnosis/\ — existing diagnosis tests
• \ ests/unit/test_cli/\ — existing CLI tests for patterns

Suggested Approach

Create \ ests/unit/test_cli/test_diagnose.py\ following existing patterns with \ yper.testing.CliRunner.

Good First Issue ✅

Good opportunity to learn both CLI testing and the diagnosis module.

[bityodha]

assigne to me