fix: make Content field editable in info panel

[Nicolass67]

Description

The Content field in the spectra editor info panel was always read-only because the ReactQuill component used a hardcoded readOnly prop. The callback also sent only the HTML string instead of the Quill Delta, so the host app could not save the content correctly.

Changes:

• Use readOnly={!canChangeDescription} so the field is editable when the host (e.g. ChemSpectra/ELN) passes canChangeDescription={true} and provides onDescriptionChanged.
• Forward all ReactQuill onChange arguments (content, delta, source, editor) so the Panel can call editor.getContents() and pass a Delta (with .ops) to the host. The content can now be saved correctly in the ELN.
• Use optional chaining for shift.ref.label in the demo to avoid runtime errors when ref is undefined.

ref: #273