v0.7.16

Standard file descriptor links

Sandbox now creates the standard Linux file descriptor links during guest init:

/dev/fd -> /proc/self/fd
/dev/stdin -> /proc/self/fd/0
/dev/stdout -> /proc/self/fd/1
/dev/stderr -> /proc/self/fd/2

This fixes common shell and tool workflows that expect /dev/fd to exist, including Bash process substitution such as cat < <(printf hi).