feat: expand c_cc[] with POSIX control character indices

feat: expand c_cc[] with POSIX control character indices

- NCCS expanded from 8 to 11
- Define VINTR(0), VQUIT(1), VERASE(2), VKILL(3), VEOF(4),
  VSUSP(7), VMIN(8), VTIME(9) with standard index values
- Initialize tty_cc[] with POSIX defaults:
  VINTR=^C, VQUIT=^\, VERASE=DEL, VKILL=^U, VEOF=^D, VSUSP=^Z
- Replace all hardcoded signal/control character comparisons in
  tty_input_char with tty_cc[] lookups
- VERASE now accepts both 0x08 (BS) and 0x7F (DEL)
- All c_cc[] entries are user-configurable via TCSETS

20/20 smoke tests pass.