test: expand test suite — 97 smoke tests, 56 host utility tests

test: expand test suite — 97 smoke tests, 56 host utility tests

- Add 8 new kernel tests to fulltest.c:
  /proc/PID/cmdline, /proc/PID/status, /dev/console, multi-pty,
  dup standalone, pipe EOF, readdir /proc, readdir /bin

- Create tests/test_host_utils.sh: host-compilable test harness for
  20 userspace utilities (echo, cat, head, tail, wc, sort, uniq, cut,
  grep, tr, basename, dirname, tee, dd, pwd, uname, id, printenv,
  cp, mv, touch, rm, mkdir, rmdir, ln) — 56 tests

- Fix echo: leading space when flags shift arg index
- Fix tail: off-by-one with trailing newline
- Fix tee/touch/cp/mv/dd: missing mode arg on open(O_CREAT)
- Fix ulibc open(): make variadic to accept optional mode

- Update smoke_test.exp with 8 new patterns (97 total)
- Add host utility tests to Makefile test-host target

Tests: 97/97 smoke, 28+19+56=103 host, cppcheck clean