Stable v2.6.62

• fix(provisioning): first site on a fresh install no longer fails + rolls back
• feat(sites): Site Doctor Phase 2 — auto-monitoring, history, more one-click fixes
• feat(sites): Site Doctor shows the actual PHP errors under collapsible details
• fix(agent): detect per-customer FPM pool by pool.conf, not template is-enabled
• fix(metrics): admin resource dashboard throttle badge is also delta-based
• feat(sites): Site Doctor Phase 1b — server-side signals, one-click PHP restart
• feat(sites): add Site Doctor — per-site health diagnosis with one-click fixes