Synchronize Folder with "#" in name results in Error

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I have searched for it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

If you try to synchronize a folder with "#" on a windows system with a nextcloud server, the client results in a bad request.
E.g. Foldername "12345678#4"
(Maybe there could a mapping inside of the client, if the server is not capable of using "#" in foldernames.)

### Steps to reproduce

1. Create folder "12345678#4" as subfolder somewhere
2. Try to add the meta folder as folder to synchronize
3. See Nextcloudclient fail to upload files in ""12345678#4""

### Expected behavior

Just syncing without problems in both directions

### Which files are affected by this bug

-

### Operating system

Windows

### Which version of the operating system you are running.

Windows 11

### Installation method

Official Linux AppImage

### Nextcloud Server version

Nextcloud Hub 26 Spring (34.0.3)

### Nextcloud Desktop Client version

34.0.3

### Did this occur after an update or on a clean installation?

Minor version update (i.e. 33.0.0 → 33.0.1)

### Are you using the Nextcloud Server Encryption module?

Yes

### Are you using an external user-backend?

- [ ] Default internal user-backend
- [ ] LDAP or Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell

```

### Additional info

_No response_

Reproduce the Windows 11 sync failure with a folder named "12345678#4" and inspect the client request or error details when uploads fail. Trace the folder-name handling in the desktop client; done means the folder synchronizes successfully in both directions without a bad request.

Written by the indexing model from the issue text.