fix(portability): make test green on macOS, GNU-only idioms replaced

The suite and seven libs assumed a GNU userland: `cmd | grep -q` under
pipefail (grep exits at the first match, the producer takes SIGPIPE,
rc 141 → 15 false "merged into" FAILs in gitflow-test), `sed -i` with no
suffix, `wc -l` padding compared as a string, `stat -c`, `touch -d`,
`realpath -m` (gstack-links refusal never fired), bare `timeout` off the
sanitized PATH (design gate READY BUT UNVERIFIED), `grep -oP` (update-all
emptied the plugin list). Thirteen suites were red on this machine.

Portable forms on the native userland of both OS: producer captured out
of the pipeline, `sed -i.bak` in tests and a temp-sibling `sed_profile`
on the user dotfile, `tr -d ' '`, python3 perms, `touch -t`, a
`realpath -m` emulation that refuses `..`, perl `alarm` for the 15 s
bound, `sed -n` token extraction. Regression tests: gstack-links T4b,
doctrine-citers Alphabet/Alpha flip, profile-set-managed T18 (failing CLI
no longer aborts `set`), new portability-census suite over the tracked
shell files. Linux run deferred (see TODO).

lib/tests/gstack-playwright.test.sh

@@ -123,8 +123,9 @@ check T7-update-conflict-nondestructive "$t7_state" "1:Y:Y"
 
 # ── T8 — no destructive command anywhere in the lib source ───────────────
 d8=OK
-sed 's/#.*//' "$L" | grep -qE 'git [^|;]*(checkout|reset|clean|stash)' && d8=BAD
-sed 's/#.*//' "$L" | grep -qwE '(rm|rmdir|unlink|truncate|mv)' && d8=BAD
+# producer out of the pipe: grep -q SIGPIPEs it under pipefail on BSD
+grep -qE 'git [^|;]*(checkout|reset|clean|stash)' < <(sed 's/#.*//' "$L") && d8=BAD
+grep -qwE '(rm|rmdir|unlink|truncate|mv)' < <(sed 's/#.*//' "$L") && d8=BAD
 check T8-no-destructive-command "$d8" OK
 
 # ── T9-T14 — browsers-report, fixture cache + playwright-core installs ───