Add tooltip hint for double-click to rename project name

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/components/projects/ProjectCard.tsx

@@ -342,6 +342,7 @@ export default function ProjectCard({ project }: Props) {
         ) : (
           <span
             className="text-sm font-medium truncate flex-1 cursor-text"
+            title="Double-click to rename"
             onDoubleClick={(e) => { e.stopPropagation(); setIsEditingName(true); }}
           >
             {project.name}