Only offer Update > Extra Themes when there is one (#7775)

* Only offer Update > Extra Themes when there is one

omarchy-theme-update pulls the themes under ~/.config/omarchy/themes that came from a git clone, so on a machine that has never installed one by hand the row opens a terminal that prints nothing and closes. Guard it with the same predicates the command itself applies, since a row that shows over a symlinked theme or a worktree's `.git` file is the same dead end in a narrower shape, and pin the two to each other in the guard test.

Co-Authored-By: Codex XHigh <noreply@openai.com>

* Extract the Extra Themes guard into omarchy-theme-extras

The row's `when:` and omarchy-theme-update each carried their own idea of which themes came from a git clone, and the two only matched because a test held them together. Name it once instead: omarchy-theme-extras lists those directories and exits nonzero when there are none, so the row asks exactly the command its action runs. Living in a script also puts the glob out of reach of whatever shopt a login shell left set for the guard batch.

Co-Authored-By: Codex XHigh <noreply@openai.com>

---------

Co-authored-by: Codex XHigh <noreply@openai.com>
(cherry picked from commit 13a969e1ab)

test/shell.d/menu-test.sh

@@ -172,6 +172,11 @@ assert(
   defaultById['update.omarchy'].iconFont === 'omarchy',
   'menu update Omarchy entry renders the private glyph with the Omarchy font'
 )
+assertEqual(
+  defaultById['update.themes'].when,
+  'omarchy-theme-extras',
+  'menu hides Extra Themes until a theme cloned from git is there to update'
+)
 assert(
   defaultById['setup.input'].action.includes('input.lua'),
   'menu keeps Input as a direct config action'