chore: consolidate and update deployment documentation

- Remove completed PRODUCTION_TODO_LIST.md
- Consolidate deployment guides: keep comprehensive PRODUCTION_DEPLOYMENT_GUIDE.md, remove redundant PRODUCTION_DEPLOYMENT.md
- Update all .env.example files to reflect current system:
  - Remove deprecated ADMIN_EMAIL/ADMIN_PASSWORD (now auto-generated)
  - Add proper documentation for all environment variables
  - Clarify that Umami config is optional (primary via Admin UI)
  - Add realistic examples for SMTP providers
  - Update ports to match actual defaults (3001)
- Update PRODUCTION_DEPLOYMENT_GUIDE.md:
  - Document auto-generated admin credentials process
  - Add Traefik configuration section
  - Update security checklist with current features
  - Fix outdated environment variables
  - Add nginx proxy configuration details

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/.env.production.example

@@ -8,7 +8,11 @@ VITE_API_URL=/api
 # For development or if frontend/backend are on different domains:
 # VITE_API_URL=https://api.yourdomain.com
 
-# Umami Analytics Configuration (optional)
-# VITE_UMAMI_URL=https://analytics.yourdomain.com
-# VITE_UMAMI_WEBSITE_ID=your-website-id-from-umami
-# VITE_UMAMI_SHARE_URL=https://analytics.yourdomain.com/share/your-share-id/photo-sharing
+# Umami Analytics Configuration (OPTIONAL - Fallback only)
+# NOTE: Primary Umami configuration should be done through Admin UI > Settings > Analytics
+# These environment variables serve as fallbacks when backend settings are not available
+# 
+# Real-world example values:
+# VITE_UMAMI_URL=https://analytics.picpeak.com
+# VITE_UMAMI_WEBSITE_ID=b4d3c2a1-5678-90ab-cdef-1234567890ab
+# VITE_UMAMI_SHARE_URL=https://analytics.picpeak.com/share/Ab3Cd5Fg/picpeak-gallery