[201_2791] Fix tab cycling issue for stroke alphabet characters

[Gitjay11]

2026/02/22 Fix Tab Cycling for Stroke Alphabet Characters.

What

Added var continuation chains for stroke alphabet characters in math-kbd.scm.

Why

To resolve issue #2791.
The tab cycling UI only displays cyclic completions for characters when they are defined through the var continuation chain from a base keystroke. Since only - var combinations were added previously, they were missing from the tab cycling menu.

How

Added ("<base> var var ..." "<#unicode>") entries corresponding to the previously added - var entries in TeXmacs/progs/math/math-kbd.scm. Also fixed minor trailing space typos in existing mappings like d - var.

How to test

1. Enter math mode.
2. Test direct shortcut: Type k then -, it should become a stroke k (<#A741>).
3. Test tab cycling: Type k then press Tab 3 times. It should correctly show the stroke k character (<#A741>) in the footer and cycle to it.
4. Repeat this tab cycling test for other base characters: c, d, f, l, o, p, s and uppercase C, D, F, K, L, O, P, S.

[da-liii]

This fix is wrong.

[Gitjay11]

hi @da-liii , can you review it now?
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