fix(newos4): piped grep searched the working directory instead of its input

The stdin work in 5cf5010 fixed wc/head/tail but left grep alone, and grep's no-operand branch
sweeps the cwd. Measured on v4.6.115: `cat /gdir/in.txt | grep zzz` answered
`other.txt:1: zzz in a cwd file` — a file that was never piped, and `cat in.txt | grep bbb`
reported the match twice (`in.txt` from the cwd sweep plus `__pipebuf__` from the injected file).

- module-fs.js: when terminal._pipeInput is set and no file operand was given, grep searches the
  staged text and prints `<line>: <text>` (stdin has no filename, as in GNU). The cwd sweep stays
  for a bare interactive `grep x`.
- shell.js: _isPipeAware now covers only sort/cut/uniq/expand. grep/head/tail/wc read _pipeInput
  themselves, so injecting the __pipebuf__ file produced duplicate hits and named stdin results.

Verification:
- test-shell-stdin.js 20 asserts (+4 for grep: no cwd match, non-match reports none, match prints
  no filename, -c counts stdin). RED on HEAD: G1/G2/G3 fail with `other.txt:1: zzz in a cwd file`.
- Suite 18/18 files; maintain --fix "node tests 18/18 pass".
- Live v4.6.116 after `cd /gdir` (where other.txt contains zzz):
  `cat /gdir/in.txt | grep zzz` -> (no matches) · `| grep bbb` -> `2: bbb` · `| grep -c b` -> 1 ·
  `| head -n 2` -> aaa,bbb · `| tail -n 1` -> ccc · `| wc -l` -> 3.

Credit: the false-positive grep was reported by the stdin subagent as an aside; re-derived here
against the live terminal before fixing.

0 files changed, 0 insertions, 0 deletions