File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Prior to 2.63.17, File Browser builds new user scopes from usernames passed through cleanUsername() when Signup=true and CreateUserDir=true, but the many-to-one normalization can collapse usernames such as team/one, team one, and team-one to the same home directory without checking whether the resulting scope is already taken, allowing a second registrant to gain full read and write access to another user's files. This issue is fixed in version 2.63.17.

Affected: Go: github.com/filebrowser/filebrowser/v2

## Summary

FileBrowser confines each user to a *scope*: a home directory that acts as the boundary for everything they can read or write. When self-registration and automatic home-directory creation are both enabled (`Signup=true` and `CreateUserDir=true`), a new user's scope is built from their username after it passes through `cleanUsername()`. That function rewrites the name: it strips `..` and replaces every character outside `0-9A-Za-z@_\-.` with `-`.

The problem is that this rewrite is **many-to-one**: different usernames can produce the same result, and FileBrowser never checks whether the resulting scope is already taken. So `team/one`, `team one`, and `team-one` all collapse to the same directory name, and whoever registers second is handed the **same home directory** as the first user instead of an isolated one.

This breaks per-user isolation. An attacker can pick a username that normalizes onto a victim's directory (for example registering `alice/` or `al..ice` to land in `alice`'s home) and gain full read **and** write access to that victim's files. Because username uniqueness is enforced on the raw name, both accounts coexist normally and neither user is warned that they share storage.

## Details

**1. The home directory is built straight from the cleaned username (`settings/dir.go:30`)**

```go // MakeUserDir, when CreateUserDir is true: username = cleanUsername(username) // ... userScope = path.Join(s.UserHomeBasePath, username) // line 30 userScope = pa…