fix: make cutover restart argv upgrade-safe and tests platform-honest

- cutover-orchestrator: restart via 'node --import tsx' (matching install.sh)
  instead of a hardcoded .pnpm/tsx@4.22.4 loader path that breaks on tsx bumps
- production-gateway: use process.execPath for the legacy-start fixture;
  POSIX-only 0600 mode assertion now win32-guarded
- cli-runtime + installer suites: skip where they require POSIX-only
  process-group SIGTERM, lsof, or /bin/sh
- fixture-safety: fall back to config.example.json when config.json is absent
  on a fresh clone

test/installer.test.js

@@ -6,7 +6,7 @@ import { test } from 'node:test';
 const installer = new URL('../scripts/install.sh', import.meta.url);
 const source = readFileSync(installer, 'utf8');
 
-test('one-click installer has safe lifecycle commands and pinned production defaults', () => {
+test('one-click installer has safe lifecycle commands and pinned production defaults', { skip: process.platform === 'win32' && 'runs /bin/sh; installer targets macOS' }, () => {
   execFileSync('/bin/sh', ['-n', installer.pathname]);
   const help = execFileSync('/bin/sh', [installer.pathname, 'help'], { encoding: 'utf8' });