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/base.html

@@ -101,7 +101,7 @@
       @dragstart="dragStart($event, {{ page.db_id }})"
       @dragover.prevent="dragOver($event, {{ page.db_id }}, {{ 'true' if page.is_folder else 'false' }})"
       @dragleave="dragLeave($event)"
-      @drop="drop($event, {{ page.db_id }})"
+      @drop.prevent="drop($event, {{ page.db_id }})"
       @dblclick="openWorkspacePage({{ page.db_id }})"
       style="padding-left:{{ 8 + depth * 16 }}px;">
     <span class="page-icon">{{ page.icon }}</span>