IRSA-7359: Fix tab navigation skipping to MathJax labels in spectrum options

[jaladh-singhal]

Fixes IRSA-7359's item-1 (item-2 is already fixed)

MathJax has a right-click menu on rendered math (with "Show Math As", "zoom", etc. options) on by default and makes every mjx-container a "Tab" keypress stop. So Tab from "Enter Redshift" in spectrum Chart options landed on the $F_\nu$ label instead of the next input. Disabled it via options.enableMenu: false in LatexUtil.jsx - not useful for our labels anyway.

Testing

https://irsa-7359-spectrum-options-mathjax-issue.irsakubedev.ipac.caltech.edu/firefly/

• (Up)load a spectrum -> open "Chart options" -> enter a redshift and press Tab -> focus should go to the "Flux axis column" input, not the $F_\nu$ label
• Tab through the rest of the dialog - no MathJax label should receive focus
• Regression: MathJax labels in the dialog and chart axis titles still render as before