Feature request: Show gradient spectrum/spectrogram to avoid forbidden resonance frequencies

[bughht]

Summary

Add a new visualization feature to display the gradient spectrum (spectrogram) during scan setup and/or execution.

Problem

Operators currently have limited visibility into how gradient energy is distributed across frequencies while configuring scan parameters. This can increase the risk of unintentionally approaching or crossing forbidden resonance frequencies.

Proposed Feature

• Add a gradient spectrum or spectrogram view.
• Overlay configurable forbidden resonance frequency bands.
• Highlight imminent or active overlap between the gradient spectrum and forbidden bands.
• Provide lightweight guidance/warnings when overlap risk is detected.

Why this matters

• Improves scan safety by making resonance risk visible before and during scans.
• Speeds up protocol tuning by giving immediate spectral feedback.
• Reduces trial-and-error and potential unsafe parameter combinations.

Acceptance Criteria

• A gradient spectrum (or spectrogram) panel is available in the UI.
• Users can define or load forbidden resonance frequency ranges.
• The UI clearly indicates when spectral content overlaps forbidden ranges.
• Visualization updates with parameter changes quickly enough to guide operator decisions.
• Documentation includes usage guidance and limitations.

Additional Notes

• Consider a compact mode for routine use and an expanded diagnostic mode for deeper analysis.
• Consider supporting both line-spectrum and time-frequency spectrogram representations, if feasible.