Add FPS recovery figure script

[zacharopoulou]

Summary

This PR adds the manuscript Figure 6 FPS recovery analysis.

Changes include:

• Added scripts/figure6_fps_recovery.py.
• Evaluates practical target recovery under the Full Pair Set (FPS).
• Uses the same missing-score rank-zero convention as Figure 5.
• Computes positive-pair recovery across prediction budgets.
• Computes precision at 50% recall for each predictor and experiment.
• Selects the best-performing predictor per experiment at 50% recall.
• Reports false positives per true positive at 50% recall.
• Writes Figure 6 panel PNG/SVG outputs and supporting TSV tables.
• Documents the Figure 6 workflow in scripts/README.md.