refactor(upload): use IncomingFile interface instead of multipart headers

Refactors the upload handler to use the `services.IncomingFile` interface instead of concrete `*multipart.FileHeader` pointers. This decouples the core upload logic from the HTTP multipart implementation, allowing for more flexible file sources.

Changes include:
- Introducing `namedMultipartFile` to adapt multipart headers to the new interface.
- Updating `createOrAppendBox`, `checkUploadPolicy`, and `totalUploadBytes` to accept `IncomingFile`.
- Renaming service calls to `CreateBoxFromIncoming` and `AppendIncomingFiles`.

backend/static/js/40-upload.js

@@ -411,7 +411,7 @@
       data: { url: window.Warpbox.absoluteURL(url || "/") },
     };
     try {
-      const registration = await navigator.serviceWorker?.ready;
+      const registration = navigator.serviceWorker ? await navigator.serviceWorker.ready : null;
       if (registration && registration.showNotification) {
         await registration.showNotification(title, options);
         return;
@@ -419,14 +419,18 @@
     } catch (error) {
       /* fall through to page notification */
     }
-    const notification = new Notification(title, options);
-    notification.onclick = () => {
-      window.focus();
-      if (url) {
-        window.location.href = window.Warpbox.absoluteURL(url);
-      }
-      notification.close();
-    };
+    try {
+      const notification = new Notification(title, options);
+      notification.onclick = () => {
+        window.focus();
+        if (url) {
+          window.location.href = window.Warpbox.absoluteURL(url);
+        }
+        notification.close();
+      };
+    } catch (error) {
+      /* notifications are best-effort */
+    }
   }
 
   function notify(variant, message, options) {
@@ -1410,8 +1414,10 @@
   function uploadFormData() {
     const formData = new FormData(form);
     formData.delete("file");
+    formData.delete("file_path");
     selectedFiles.forEach((file) => {
       formData.append("file", file, uploadName(file));
+      formData.append("file_path", uploadName(file));
     });
     return formData;
   }