fix: eliminate resource-collision race in ship-notes-wedged-pr jq() mock

Unrelated defect surfaced by a real gsd-test failure while verifying
#3339 (test/3339-fold-state-model-profile diffs zero files this fix
touches -- confirmed via `git diff <this-branch> origin/next -- ...`
returning empty for this file, ship.md, and gsd-core/bin/lib/*.cjs).
Fixed inline per this repo's no-defer policy for defects found while
building, rather than deferred.

The test's jq() mock shelled out to a full new Node.js process for
every mocked `jq -r .field` call inside the extracted track_shipping
bash script. The "exhausts the polling bound" test hits up to 24 cold
Node spawns in one spawnSync call (6 polling iterations x 4 jq calls),
racing a hardcoded 10s timeout -- under CI contention this tipped over
on the linux-node22 lane specifically while linux-node24 had headroom,
producing spawnSync's signal-killed `status: null` instead of the
process's real exit code, asserted against the expected 0.

Replaced the Node-subprocess jq() mock with a pure-shell sed -nE field
extractor that never forks a process, eliminating the variable-cost
operation rather than just widening the timeout. Verified extraction
correctness against sample JSON (head/status/checks/review, including
empty-string and non-matching-field cases). Locally verified (scoped
per session policy): all 9 tests in the file pass; the previously-
marginal test dropped from ~617ms to ~198ms.

The underlying track_shipping polling logic in ship.md was confirmed
correct and untouched -- this was a test-fixture race, not a product
bug.

tests/ship-notes-wedged-pr.test.cjs

@@ -62,7 +62,11 @@ function runTrackShipping(responses) {
       '  sed -n "${_call}p" "$GH_RESPONSES"',
       '}',
       'jq() {',
-      '  "$NODE_BIN" -e "let d=\'\';process.stdin.on(\'data\',c=>d+=c);process.stdin.on(\'end\',()=>{const o=JSON.parse(d);process.stdout.write(String(o[process.argv[1].slice(1)] ?? \'\'));});" "$2"',
+      '  _field="${2#.}"',
+      '  _raw=$(sed -nE \'s/.*"\'"$_field"\'":("[^"]*"|[^,}]*).*/\\1/p\')',
+      '  _raw="${_raw%\\"}"',
+      '  _raw="${_raw#\\"}"',
+      '  printf \'%s\' "$_raw"',
       '}',
     ].join('\n');
 
@@ -77,7 +81,6 @@ function runTrackShipping(responses) {
         GH_CALLS: ghCallsPath,
         GH_RESPONSES: responsesPath,
         GIT_CALLS: gitCallsPath,
-        NODE_BIN: process.execPath,
         PHASE_NUMBER: '1',
         PR_NUMBER: '123',
         padded_phase: '01',