fix: drag & drop — add .prevent modifier to @drop handlers

Both sidebar and workspace page DnD handlers now use @drop.prevent
to stop browser's default text insertion behavior. Without .prevent,
the browser tries to navigate to the dragged text as a URL, breaking
the drop event.

app/templates/local_workspace.html

@@ -82,7 +82,7 @@
              @dragstart="dragStart($event, node.db_id)"
              @dragover.prevent="dragOver($event, node.db_id, node.is_folder)"
              @dragleave="dragLeave($event)"
-             @drop="doDrop($event, node.db_id)">
+             @drop.prevent="doDrop($event, node.db_id)">
           <span class="chevron" x-show="node.is_folder" @click.stop="toggleFolder(node)">▶</span>
           <span class="icon" x-text="node.icon"></span>
           <span class="name" x-text="node.name" @dblclick="rename(node)"></span>