fix: resolve critical production deployment issues

- Fix database connection error "getaddrinfo ENOTFOUND postgres"
- Add wait-for-db.sh script to ensure PostgreSQL is ready before starting
- Fix email processor initialization timing issue
- Add missing storage path environment variables
- Add database dependency to backend service
- Enhance health check endpoint with database connectivity check
- Update production database defaults to match docker-compose
- Install postgresql-client in Docker image for health checks
- Document all required environment variables in .env.example

Fixes immediate production deployment failures and ensures proper service startup order.

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

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

backend/Dockerfile

@@ -16,8 +16,8 @@ FROM node:18-alpine
 
 WORKDIR /app
 
-# Install dumb-init for proper signal handling
-RUN apk add --no-cache dumb-init
+# Install dumb-init for proper signal handling and postgresql-client for database checks
+RUN apk add --no-cache dumb-init postgresql-client
 
 # Create non-root user
 RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001
@@ -26,6 +26,9 @@ RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001
 COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
 COPY --chown=nodejs:nodejs . .
 
+# Make wait script executable
+RUN chmod +x wait-for-db.sh
+
 # Create necessary directories
 RUN mkdir -p storage/events/active storage/events/archived storage/thumbnails data logs && \
     chown -R nodejs:nodejs storage data logs
@@ -35,4 +38,4 @@ USER nodejs
 EXPOSE 3000
 
 ENTRYPOINT ["dumb-init", "--"]
-CMD ["node", "server.js"]
+CMD ["./wait-for-db.sh", "node", "server.js"]