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/floor-guard.test.sh

@@ -101,7 +101,8 @@ check_kind STUB "$rc" 2 "$out" 'FLOOR STUB'
 
 # ── THRESHOLD_DOWN ────────────────────────────────────────────────────────
 d=$(mk_repo threshold); base=$(git -C "$d" rev-parse HEAD)
-sed -i 's/lines: 80/lines: 60/' "$d/vitest.config.ts"
+# BSD sed -i needs a suffix argument
+sed -i.bak 's/lines: 80/lines: 60/' "$d/vitest.config.ts" && rm -f "$d/vitest.config.ts.bak"
 out=$(cd "$d" && bash "$LIB" "$base" 2>&1); rc=$?
 check_kind THRESHOLD_DOWN "$rc" 2 "$out" 'FLOOR THRESHOLD_DOWN'