Make worktree banner name clickable to copy to clipboard

Clicking the worktree name in the banner now copies it to clipboard
and shows "Copied\!" feedback for 1.5 seconds.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/WorktreeBanner.tsx

@@ -1,7 +1,18 @@
+import { useCallback, useState } from "react";
 import { getWorktreeUiBranding } from "../lib/worktree-branding";
 
 export function WorktreeBanner() {
   const branding = getWorktreeUiBranding();
+  const [copied, setCopied] = useState(false);
+
+  const handleCopyName = useCallback(() => {
+    if (!branding) return;
+    navigator.clipboard.writeText(branding.name).then(() => {
+      setCopied(true);
+      setTimeout(() => setCopied(false), 1500);
+    });
+  }, [branding]);
+
   if (!branding) return null;
 
   return (
@@ -18,7 +29,14 @@ export function WorktreeBanner() {
       <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>
+        <button
+          type="button"
+          onClick={handleCopyName}
+          title="Click to copy worktree name"
+          className="truncate font-semibold tracking-[0.12em] cursor-pointer hover:opacity-80 transition-opacity bg-transparent border-none p-0 text-current uppercase text-[11px]"
+        >
+          {copied ? "Copied!" : branding.name}
+        </button>
       </div>
     </div>
   );