fix: disable Tauri file drop handler — unblocks HTML5 drag-and-drop

Tauri's built-in dragDropEnabled intercepts all drag events in the
WebView for native file drop handling. This prevents HTML5 drag-and-drop
between elements within the page. Disabled so tab reordering works.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -17,7 +17,8 @@
         "minWidth": 800,
         "minHeight": 600,
         "decorations": true,
-        "resizable": true
+        "resizable": true,
+        "dragDropEnabled": false
       }
     ],
     "security": {