fix: pair-agent skill compliance + fix all 16 pre-existing test failures

Root cause: pair-agent was added without completing the gen-skill-docs
compliance checklist. All 16 failures traced back to this.

Fixes:
- Sync package.json version to VERSION (0.15.9.0)
- Add "(gstack)" to pair-agent description for discoverability
- Add pair-agent to Codex path exception (legitimately documents ~/.codex/)
- Add CLI_COMMANDS (status, pair-agent, tunnel) to skill parser allowlist
- Regenerate SKILL.md for all hosts (claude, codex, factory, kiro, etc.)
- Update golden file baselines for ship skill
- Fix relink tests: pass GSTACK_INSTALL_DIR to auto-relink calls so they
  use the fast mock install instead of scanning real ~/.claude/skills/gstack

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/gen-skill-docs.test.ts

@@ -1739,7 +1739,10 @@ describe('Codex generation (--host codex)', () => {
   test('Claude output unchanged: all Claude skills have zero Codex paths', () => {
     for (const skill of ALL_SKILLS) {
       const content = fs.readFileSync(path.join(ROOT, skill.dir, 'SKILL.md'), 'utf-8');
-      expect(content).not.toContain('~/.codex/');
+      // pair-agent legitimately documents how Codex agents store credentials
+      if (skill.dir !== 'pair-agent') {
+        expect(content).not.toContain('~/.codex/');
+      }
       // gstack-upgrade legitimately references .agents/skills for cross-platform detection
       if (skill.dir !== 'gstack-upgrade') {
         expect(content).not.toContain('.agents/skills');