feat: add separator component

Horizontal and vertical separator (divider) with CSS classes, ARIA
role="none", and data-orientation attribute. Includes dark mode support,
unit tests, and demos in all three dev targets.

src/ui/separator.cljc

@@ -0,0 +1,53 @@
+(ns ui.separator
+  (:require [clojure.string :as str]))
+
+#?(:squint (defn- kw-name [s] s)
+   :cljs   (defn- kw-name [s] (name s))
+   :clj    (defn- kw-name [s] (name s)))
+
+(defn separator-class-list
+  "Generate a vector of CSS class strings for a separator.
+   Orientation: :horizontal (default), :vertical."
+  [{:keys [orientation]}]
+  (let [o (or (some-> orientation kw-name) "horizontal")]
+    ["separator" (str "separator-" o)]))
+
+(defn separator-classes
+  "Generate CSS class string for a separator."
+  [opts]
+  (str/join " " (separator-class-list opts)))
+
+(defn separator
+  "Render a separator element. Works across all targets via reader conditionals.
+
+   Props:
+     :orientation - :horizontal (default), :vertical
+     :class       - additional CSS classes
+     :attrs       - additional HTML attributes map"
+  [{:keys [orientation class attrs] :as _props}]
+  #?(:squint
+     (let [classes (cond-> (separator-classes {:orientation orientation})
+                     class (str " " class))
+           base-attrs (merge {:class classes
+                              :role "none"
+                              :data-orientation (or (some-> orientation kw-name) "horizontal")}
+                             attrs)]
+       [:div base-attrs])
+
+     :cljs
+     (let [cls (separator-class-list {:orientation orientation})
+           classes (cond-> cls class (conj class))
+           base-attrs (merge {:class classes
+                              :role "none"
+                              :data-orientation (or (some-> orientation kw-name) "horizontal")}
+                             attrs)]
+       [:div base-attrs])
+
+     :clj
+     (let [classes (cond-> (separator-classes {:orientation orientation})
+                     class (str " " class))
+           base-attrs (merge {:class classes
+                              :role "none"
+                              :data-orientation (or (some-> orientation kw-name) "horizontal")}
+                             attrs)]
+       [:div base-attrs])))

src/ui/separator.css

@@ -0,0 +1,27 @@
+/* Separator — visually or semantically separates content */
+
+.separator {
+  flex-shrink: 0;
+  background: var(--gray-200);
+}
+
+.separator-horizontal {
+  height: 1px;
+  width: 100%;
+}
+
+.separator-vertical {
+  width: 1px;
+  align-self: stretch;
+}
+
+/* Dark mode: use a lighter border shade */
+[data-theme="dark"] .separator {
+  background: var(--gray-800);
+}
+
+@media (prefers-color-scheme: dark) {
+  :root:not([data-theme="light"]) .separator {
+    background: var(--gray-800);
+  }
+}