XY-833: [ELF operator UX P1] Fix real-world operator-debugging failure cases

[yvette-carlisle]

Summary

• Repair operator-debugging fixtures so dropped expected evidence and stage attribution are backed by expected trace evidence, not decoy produced evidence.
• Add trace_explainability for the dropped-evidence filter stage and keep decoys visible in stage-level trace metadata.
• Update real-world benchmark assertions and operator UX report docs.

Verification

• cargo test -p elf-eval --test real_world_job_benchmark --all-features
• cargo make real-world-job-operator-ux
• cargo make real-world-memory
• cargo make fmt
• cargo make lint-fix
• cargo make checks