feat(ui-theme): default the theme fallback to bundled dupre

The fallback kicks in when persist/emacs-theme is missing — a fresh machine, or one that's never saved a theme. It was modus-vivendi, which ships with Emacs but has none of the dimming colors this config chooses, so an unconfigured machine looked and dimmed differently from a configured one. I hit exactly that on a second box this week.

dupre is bundled in themes/ and carries those colors, and it loads wherever this config does, so it's the better default. I added a regression test asserting the default is dupre; its loadability is already covered by test-dupre-theme.el. The docstring no longer claims the fallback must be a built-in theme, since dupre isn't one.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/test-ui-theme-commands.el b/tests/test-ui-theme-commands.el
index f5f57c319..55facc17e 100644
--- a/tests/test-ui-theme-commands.el
+++ b/tests/test-ui-theme-commands.el
@@ -34,6 +34,16 @@
         (fallback-theme-name "modus-vivendi"))
     (should (equal "modus-vivendi" (cj/get-active-theme-name)))))
 
+;;; fallback-theme-name default
+
+(ert-deftest test-ui-theme-default-fallback-is-bundled-dupre ()
+  "Normal: the default fallback theme is dupre, the config's bundled theme.
+modus-vivendi ships with Emacs but has no chosen dimming colors; dupre is
+bundled in themes/, so it is available on every machine that loads this
+config and is the right default fallback.  Its loadability is covered by
+test-dupre-theme.el."
+  (should (equal "dupre" (default-value 'fallback-theme-name))))
+
 ;;; cj/save-theme-to-file
 
 (ert-deftest test-ui-theme-save-writes-active-name-to-file ()