Document the separator (#210)

* Document the separator

Basecoat has no Separator component: an <hr> already renders as a 1px line in the border color. Add a docs page with horizontal, vertical, menu, list and RTL examples that mirror shadcn/ui's Separator docs.

* Style vertical separators in base CSS

Add a low-specificity base rule so <hr aria-orientation="vertical"> renders
as a 1px inline-start line that stretches to its row, matching shadcn/ui's
vertical Separator. Rewrite the Separator docs to use it without utility
classes, note role="none" for decorative separators, and add a changelog
entry.

---------

Co-authored-by: grugbraindev <178141691+grugbraindev@users.noreply.github.com>

src/css/base/base.css

@@ -133,4 +133,13 @@
   body {
     @apply bg-background text-foreground overscroll-none;
   }
+  hr:where([aria-orientation='vertical']) {
+    flex-shrink: 0;
+    align-self: stretch;
+    inline-size: 1px;
+    block-size: auto;
+    margin: 0;
+    border-block-start-width: 0;
+    border-inline-start-width: 1px;
+  }
 }