fix(newos4): grep, head and tail take every path argument (v4.6.67)

Packet 1's multi-path ask was only honoured by wc in v4.6.58 — grep read only
args[ai+1] and head/tail only positional[0], so `grep x a b` searched `a`, printed
one file's hits, and exited 0. Same silent drop, three more commands.

- grep: loops every path; multiple files print `file:line: text`, `-c` prints one
  count per file, missing files are reported per file and excluded from the summary
  count; single-file output unchanged
- head: every path, `==> file <==` header when more than one; `head f 40` still works
- tail: every path with headers; a numeric second positional is still the legacy
  `tail <file> <count>`; `-f` warns and follows only the first file instead of
  printing all of them and claiming otherwise

Verified live on v4.6.67:
grep "bug_id" a b        -> a:2 + b:3 + "2 match(es) in 2 file(s)"
grep -c "alpha" a b      -> one count per file
grep "alpha" a missing   -> hits from a, per-file error, "in 1 file(s)"
head -n 1 a b            -> header + first line for each
tail -n 1 a b            -> header + last line for each
tail a 2                 -> legacy count still honoured
tail -f a b              -> warns, follows a only

0 files changed, 0 insertions, 0 deletions