feat: support multi-spectrum comparison in SpectraEditor

[Nicolass67]

Summary

This PR adds multi-spectrum comparison support to @complat/react-spectra-editor

What this enables

• Comparison modal workflow: the ELN passes multiple JCAMP entities; the editor loads them via MultiJcampsViewer and renders them in the multi-curve viewer (d3_multi).
• Active spectrum selection: a graph selection panel lets users pick which curve is being edited; toolbar actions and annotations apply to that curve.
• Per-curve state: shift, peaks, integrations, multiplicities, and threshold are tracked per spectrum, so calibration and annotations stay correct when switching between overlaid curves.
• Layout-aware UI: toolbar controls that do not apply to the current layout (NMR, HPLC, CV, etc.) are hidden rather than disabled.
• HPLC support: improved formatting and display of retention times and AUC values in comparison mode.
• Save/submit: write-back uses the active curve index so saved data matches the spectrum the user was working on

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