test(W7h): pin the Codex availability probe free for the four offering skills

Replacement check for the codex-offered-* paid retirement (t14 F8): each of
office-hours, plan-ceo-review, plan-design-review and plan-eng-review must
render the executed `command -v codex` probe and its `not_installed`
fallback mode in its generated SKILL.md + sections. These are bash lines the
agent runs, so a deterministic grep replaces a paid model summary of them.
skill-validation.test.ts already covers the default-on outside voice for
eng/CEO/devex; this adds office-hours and plan-design-review and the
fallback token.

Control (scratch worktree, generated files): removing the probe from
office-hours, plan-design-review or plan-eng-review, or the CEO
not_installed branch, turns the new test red (4/4). Log:
.context/mutation-codex-offering.md.

test/gen-skill-docs.test.ts

@@ -1838,6 +1838,16 @@ describe('Codex filesystem boundary', () => {
   });
 });
 
+// --- Codex outside-voice availability probe ---
+
+describe('Codex outside voice is offered behind an executed availability probe', () => {
+  test.each(['office-hours', 'plan-ceo-review', 'plan-design-review', 'plan-eng-review'])('%s probes codex and has a not-installed fallback', skill => {
+    const content = readSkillUnion(skill);
+    expect(content).toContain('command -v codex');
+    expect(content).toContain('not_installed');
+  });
+});
+
 // --- {{BENEFITS_FROM}} resolver tests ---
 
 describe('BENEFITS_FROM resolver', () => {