feat: support folder uploads and sanitize upload paths

- Implement `cleanUploadDisplayName` in the backend to safely sanitize uploaded file paths, preserving directory structures while stripping unsafe characters and preventing path traversal.
- Add folder upload capability in the frontend using the Directory Picker API.
- Implement desktop notifications for completed uploads.

backend/static/js/service-worker.js

@@ -5,6 +5,26 @@ self.addEventListener("fetch", (event) => {
   }
 });
 
+self.addEventListener("notificationclick", (event) => {
+  event.notification.close();
+  const url = event.notification.data && event.notification.data.url ? event.notification.data.url : "/";
+  event.waitUntil((async () => {
+    const windows = await clients.matchAll({ type: "window", includeUncontrolled: true });
+    for (const client of windows) {
+      if ("focus" in client) {
+        await client.focus();
+        if ("navigate" in client) {
+          await client.navigate(url);
+        }
+        return;
+      }
+    }
+    if (clients.openWindow) {
+      await clients.openWindow(url);
+    }
+  })());
+});
+
 const SHARE_CACHE = "warpbox-share-target-v1";
 const SHARE_PREFIX = "/__warpbox_share_target__/";
 const LATEST_KEY = SHARE_PREFIX + "latest";