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>

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>