Fix: Hotspot Index Out-of-Bounds Error in Nanobody Sampling

[RicardoZF]

Problem:

• hotspot_index was calculated on the full structure (including non-standard residues)
• Data is later filtered by modeled_idx (keeping only standard amino acids)
• Saved hotspot indices were not mapped to the filtered space
• This caused IndexError when indices exceeded the filtered array size

Example:

• Original structure: 196 residues
• After filtering: 188 residues (modeled_seq_len)
• Hotspot indices: [146, 157, 173, 179] (based on original structure)
• Error: index 179 > 188, out of bounds

Solution:
Map hotspot indices to the modeled_idx space before saving to metadata.