v3.8.109

tina4 CLI 3.8.109

- #129: tina4 serve names the missing vendor/bin/tina4php and says
  'Run: composer install' when php is on PATH but the launcher is absent
  (follow-up to #127), instead of a bare 'program not found'.
- Metrics gate unblocked: re-baselined .tina4-metrics.json + pinned the gate
  tool to v3.8.108 (was red on main since the Oct-19 metrics/ engine split).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>