🐛 Use a single translation key for the Mixed values label (#11151)

The design sidebar named the same "mixed values" concept with two
different translation keys. Most sections use settings.multiple, while
the blur options and the design system numeric input used
labels.mixed-values.

Both read "Mixed" in English, so the split is invisible in the default
locale, but labels.mixed-values has no translation at all in 16 locales
and a different wording in 8 more. Where it is missing the string falls
back to the default language, so those controls rendered the English
word next to sections showing the localized one; where both exist, a
single sidebar named the same concept two ways (fr "Divers" against
"Melange", ru "Smeshanyy" against "Smeshat").

Point the two outliers at settings.multiple, the key the rest of the
sidebar already uses and the one translated in every locale that ships
a translation for it.

Fixes #11148.

Signed-off-by: Filip Sajdak <filip.sajdak@siili.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

frontend/src/app/main/ui/ds/controls/numeric_input.cljs

@@ -723,7 +723,7 @@
                                 :id id
                                 :class inner-class
                                 :placeholder (if is-multiple?
-                                               (tr "labels.mixed-values")
+                                               (tr "settings.multiple")
                                                placeholder)
                                 :default-value (fmt/format-number (or (mf/ref-val last-value*) value))
                                 :on-blur handle-blur

frontend/src/app/main/ui/workspace/sidebar/options/menus/blur.cljs

@@ -296,7 +296,7 @@
         (if mixed-state
           [:div  {:class (stl/css :first-row)}
            [:span {:class (stl/css :mixed-label)}
-            (tr "labels.mixed-values")]
+            (tr "settings.multiple")]
            [:> icon-button* {:variant "ghost"
                              :aria-label (tr "workspace.options.blur-options.remove-blur")
                              :on-click handle-delete-all