2026/02/21 Support \bold command

What

Added support for the \bold command within the LaTeX plugin's import logic.

Why

To Fix issue #2827 @da-liii
The original LaTeX parser treated \bold as an undefined macro during import. This resulted in an unsupported red tag appearing in the Mogan editor.

How

1. In TeXmacs/plugins/latex/progs/convert/latex/latex-command-drd.scm, registered bold in the latex-modifier-1% logic group so the parser recognizes it as a standard single-argument formatting macro.
2. In TeXmacs/plugins/latex/progs/convert/latex/tmtex.scm, added a proxy translation rule inside post-process-math-text: ((func? t 'bold 1) (post-process-math-text (list 'mathbf (cadr t)))). This intercepts \bold and delegates it to \mathbf, ensuring that it inherits all necessary logic for properly rendering both text and math content into bold.

How to test

1. Create a LaTeX file containing \bold{test}.
2. Import the file into .tm format.
3. Verify that the imported document correctly renders "test" in bold text, identical to how \mathbf{test} is normally handled, instead of showing a raw red \bold tag.