Linux host TTY input

We switched back from AtomVM to Linux bring-up and double-checked that userspace hello was already captured in the P62/P64/P66 Linux logs. So P79 is not “first userspace”; it is the missing input side of the existing HVC console.

The implementation is narrow:

• top-level host input pins;
• a 16-entry MMIO FIFO at 0x10001008/0x1000100c;
• SBI_CONSOLE_GETCHAR reads that FIFO instead of always returning -1;
• a project-local Verilator harness reads bytes from a host FIFO;
• a tiny no-libc /init loops on read(0, ...).

The first smoke passed. Linux booted to /init, accepted scripted help, status, hello, and exit commands, then hit the expected PID 1 exit panic. The harness reported:

[harness] input bytes read=23 delivered=23 queued=0

One boring snag: /tmp/gen_init_cpio was gone. The P79 userspace Makefile now builds the kernel tree’s usr/gen_init_cpio helper directly when needed.

BusyBox is the obvious next Linux project, but it should come after this transport proof. Now that fd 0 works, BusyBox becomes rootfs and kernel-config work instead of console debugging.