Drop /dev/input aggregator, procfs cwd and umask
* Remove kernel input.c/h; keyboard and mouse each manage their own
wait queue, poll callback, and blocking read with EINTR/EAGAIN
support; rename /dev/kbd to /dev/keyboard
* Add procfs cwd and umask entries: sched_proc_cwd() copies thread
cwd under lock, sched_getumask/sched_setumask mirror the umask
field; expose umask as octal in the stat file
* Remove SYS_GETCWD and SYS_UMASK syscalls; re-implement getcwd()
and umask() in libc_usr via /proc/self/cwd and /proc/self/umask;
renumber remaining syscall table entries
* Replace ui_t input_fd with keyboard_fd + mouse_fd; ui_input() reads
key_event/mouse_event structs directly, translates to input_event_t
inline with modifier tracking and round-robin fairness
* Expand WM poll loop from 2 to 3 fds (keyboard, mouse, wm manager)