Remove stale Volcano v85 function file

[maggiecam]

Summary

• Remove the stale Volcano_Plot_Enhanced_v85.R file after the Code Ocean rename to Volcano_Plot_Enhanced.R
• Update Volcano module metadata and developer docs to reference the current function filename
• Update the Volcano smoke test to match the current CLI and clean generated PNG outputs

Validation

• Rscript tests/test-module-contract.R
• modules/volcano/runtime/tests/test_run_small.sh
• git diff --check

This follow-up keeps main aligned with the current Code Ocean capsule layout after PR #8.