Create standard devices for command line runs

[siraben]

Summary

Create standard /dev nodes during command-line emulator startup.

The iOS app startup already creates /dev/ptmx, but the CLI path only mounted
devpts at /dev/pts. Static i386 tmux could start and parse commands, but
failed when creating the first pane because forkpty could not open the pty
master:

create window failed: fork failed: No such file or directory

This moves the existing standard device-node setup into shared kernel init code
and calls it from both app and CLI startup. The CLI path now gets /dev/ptmx
before mounting devpts, without duplicating the app's /dev setup list.

Validation

• ninja -C build
• Removed /dev/ptmx from the Alpine test filesystem, then confirmed the
  rebuilt CLI emulator recreated it on startup.
• Ran static i386 tmux in Alpine:
  • tmux -V
  • tmux -h
  • tmux -L final-smoke -f /dev/null new-session -d /bin/true

[tbodt]

theoretically the correct solution is to create an implementation of devtmpfs instead of creating device nodes like this. (i don't think I knew about devtmpfs at the time)