Improve host-shell cleanup and status handling

[midwan]

Summary

• return an error when host-shell cannot open dos.library, console IO, raw input mode, or the host shell session
• use a single cleanup path for host shell close, raw mode restoration, and library cleanup
• propagate HostShell_Status when available so host-shell can report host command failure
• remove the unused loop flag and preserve a pending trailing ESC byte during cleanup

Validation

• make -B test HOST_CFLAGS="-std=c99 -Wall -Wextra -Wstrict-prototypes -Werror -Isrc"
• git diff --check