[202_2723] Add tooltips for overbrace underbrace underline

[Gitjay11]

2026/02/24 Add tooltips for overbrace, underbrace, and underline

What

Added missing text-based balloon widgets for \overbrace, \underbrace, and \underline to the math-insert-icons menu in [math-menu.scm].

Why

The mode toolbar's accent popup was missing these corresponding options, meaning users had no tooltips or UI buttons for inserting wide braces or underlines from the toolbar. This resolves issue #2723.

How

Modified [TeXmacs/progs/math/math-menu.scm] to append three new entries to the tm_wide tile grid within math-insert-icons. They use text labels \overbrace, \underbrace, and \underline and are mapped to (make-wide "<wide-overbrace>"), (make-wide-under "<wide-underbrace>"), and (make-wide-under "<wide-bar>") respectively.

How to test

1. Open Mogan and enter a math environment ($).
2. Long press or click the "Wide accents" toolbar icon (the ~ on the mode toolbar).
3. Verify that \overbrace, \underbrace, and \underline are present in the popup menu.
4. Hover over them to see the translated tooltips and shortcuts.
5. Click them to verify they insert the correct macros.

[Gitjay11]

hii @da-liii @JackYansongLi , When you have time, please review this PR and let me know if any changes are needed, Thank you.