Add worktree UI branding

ui/src/components/WorktreeBanner.tsx

@@ -0,0 +1,25 @@
+import { getWorktreeUiBranding } from "../lib/worktree-branding";
+
+export function WorktreeBanner() {
+  const branding = getWorktreeUiBranding();
+  if (!branding) return null;
+
+  return (
+    <div
+      className="relative overflow-hidden border-b px-3 py-1.5 text-[11px] font-medium tracking-[0.2em] uppercase"
+      style={{
+        backgroundColor: branding.color,
+        color: branding.textColor,
+        borderColor: `${branding.textColor}22`,
+        boxShadow: `inset 0 -1px 0 ${branding.textColor}18`,
+        backgroundImage: `linear-gradient(90deg, ${branding.textColor}14, transparent 28%, transparent 72%, ${branding.textColor}12), repeating-linear-gradient(135deg, transparent 0 10px, ${branding.textColor}08 10px 20px)`,
+      }}
+    >
+      <div className="flex items-center gap-2 overflow-hidden whitespace-nowrap">
+        <span className="shrink-0 opacity-70">Worktree</span>
+        <span className="h-1.5 w-1.5 shrink-0 rounded-full bg-current opacity-70" aria-hidden="true" />
+        <span className="truncate font-semibold tracking-[0.12em]">{branding.name}</span>
+      </div>
+    </div>
+  );
+}