Feature detail pages with improved cross-linking and SEO

Features

• Feature detail pages with improved cross-linking and SEO
• Features hub and A/B testing page with experiments dashboard
• Startup environment validation across all apps
• Agent-facing domain endpoints with Domain Connect auto-verification
• On/off toggles for humanizer and human-in-the-loop in mailbox settings
• Sent emails now linked to threads for better conversation tracking

Fixes

• Fixed tenant scoping on experiment endpoints to prevent cross-tenant access
• Fixed human-in-the-loop approval auth and inbox filtering
• Fixed Docker builds missing the env package