Shifted-clock job: fix the two test-harness clock artefacts (git commit dates, claude-account-script env) so it is green with nothing skipped #800

Outcome: the weekly shifted-clock job (#687 / PR #774) is green at +45d and +400d without marking or skipping any test. The two test-harness artefacts it found are fixed in the test harness, not in the product.

Why (measured by #774's builder and round-2 review, run 39204725103):

• test/pr-hygiene-coordinator.test.ts, lines 20 and 60, both shifts. The coordinator reads commit times with git log --format=%ct, and git stamps the test's commits with the real clock while Node's clock is shifted.
  • Measured: giving the harness's git helper commit dates from Node's Date.now() (GIT_AUTHOR_DATE/GIT_COMMITTER_DATE) makes the file pass 6/6 at +45d, at +400d and on the real clock.
• test/claude-account-script.test.ts, the "a year" check at line 183, +400d only. expiresAt is written by a Node child of scripts/setup/lib.sh:625. The test starts the script with env: { PATH, HOME } only (line 136), which drops NODE_OPTIONS and TEST_CLOCK_SHIFT.
  • Measured: passing both through gives 22/22 at +400d.
• The third failure, dashboard-switch-speed, is the known flake dashboard-switch-speed: say which check failed; keep a shown Board when one fresh read fails (rare flake) #639 and stays there.

Do:

1. In the test harness's git helper(s), set the commit and author dates from Node's clock.
2. In claude-account-script's test, pass NODE_OPTIONS and TEST_CLOCK_SHIFT through to the script's environment.
3. Show the weekly job green at both shifts, apart from dashboard-switch-speed: say which check failed; keep a shown Board when one fresh read fails (rare flake) #639 if it recurs, on the PR.

Constraints:

• Test harness only. No product change, no skip, no mark.
• Every assertion is unchanged (rule 10).

Review point: test harness. Routine unless a file is in engine-guards.

Related: #687, #774, #639.