Surface red team scan errors in run results

[slister1001]

When all attacks fail due to a configuration error (e.g., unavailable model), the run previously completed with 0 results and no error message. Users had no way to understand what went wrong.

Changes:

• Add error field to RedTeamRun TypedDict for run-level error reporting
• Add _aggregate_run_errors() to ResultProcessor to collect per-category errors from red_team_info into a structured run-level error
• Classify HTTP 400 as CONFIGURATION in ExceptionHandler so systemic config errors (unavailable_model, bad credentials) are detected
• Add early abort in Foundry execution manager after 2 consecutive configuration errors to avoid wasting time on remaining categories
• Add _is_configuration_error() helper to detect systemic issues

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