Uploading more than one image from iOS shortcut only uploads first image

### Describe the bug
When attempting to upload more than one image to copyparty using the iOS shortcut, only the first image is uploaded, even though the shortcut asks for permission to upload multiple photos.

### To Reproduce
Select more than one photo in iOS phone gallery and tap share, and use the share to copyparty shortcut

### Expected behavior
All images should be uploaded to copyparty

### Screenshots
if applicable, add screenshots to help explain your problem, such as the kickass crashpage :^)

### Server details (if you're NOT using docker/podman)
remove the ones that are not relevant:
* **server OS / version:** Windows 10 21H2
* **what copyparty did you grab:** Python
* **how you're running it:** Double clicking the python file
* run copyparty with `--version` and grab the last 3 lines (they start with `copyparty`, `CPython`, `sqlite`) and paste them below this line:
* copyparty v1.19.21 "usernames" (2025-12-02)
CPython v3.14.0 on Windows64 10.0.19044 [MSC v.1944 64 bit (AMD64)]
sqlite 3.50.4*1 | jinja 2.11.3 | pyftpd 1.5.10 | tftp 0.4.0
* **copyparty arguments and/or config-file:**

### Client details
if the issue is possibly on the client-side, then mention some of the following:
* the device type and model: iPhone 14
* OS version: iOS 17.6.1
* browser version: N/A

### The rest of the stack
if you are connecting directly to copyparty then that's cool, otherwise please mention everything else between copyparty and the browser (reverseproxy, tunnels, etc.)

### Server log
if the issue might be server-related, include everything that appears in the copyparty log during startup, and also anything else you think might be relevant

### Additional context
any other context about the problem here

copyparty の iOS shortcut integration と upload handling code を見てください。この issue はおそらく、shortcut の share sheet から複数のファイルがどのように処理されるかに関係しています。uploads を受け取る HTTP endpoint を調べることから始め、multipart/form-data の handling を確認し、request にすべてのファイルが含まれているかを見てください。iOS shortcut からの multi-file upload をシミュレートするか、複数ファイルで curl を使用して再現してください。upload 試行中の server logs を確認し、すべてのファイルが受信されているかを見てください。

索引モデルが issue の本文から書いたものです。