feat: Preserve signature names + improve high-res decomposition stability

[mdbarnesUCSD]

• Feature: Preserve original user-provided signature names throughout decomposition (logs, mapping CSV, plots, Activities/Signatures outputs) instead of replacing them with generic IDs.
• Fix: Corrected collapse_to_SBS96 so both the numeric matrix and originalProcessAvg metadata collapse consistently, preventing dimension mismatches for SBS288/SBS1536.
• Stability: Skip decomposition plot generation when running SBS288/SBS1536 with collapse_to_SBS96=False to avoid unsupported high-resolution plotting errors.
• Refactor: Capture input dataframes in spa_analyze before NumPy conversion to avoid metadata loss.
• Minor: Fixed typos in comments and logs.