CVE-2026-35607: File Browser: Proxy auth auto-provisioned users inherit Execute permission and Commands

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Prior to 2.63.1, the fix in commit b6a4fb1 ("self-registered users don't get execute perms") stripped Execute permission and Commands from users created via the signup handler. The same fix was not applied to the proxy auth handler. Users auto-created on first successful proxy-auth login are granted execution capabilities from global defaults, even though the signup path was explicitly changed to prevent execution rights from being inherited by automatically provisioned accounts. This vulnerability is fixed in 2.63.1.