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/src/services/emailProcessor.js

@@ -395,12 +395,15 @@ function stopEmailQueueProcessor() {
   }
 }
 
-// Initialize on module load
-initializeTransporter().then(() => {
-  startEmailQueueProcessor();
-});
+// Initialize on module load - DISABLED for production startup
+// This will be called from server.js after database is ready
+// initializeTransporter().then(() => {
+//   startEmailQueueProcessor();
+// });
 
 module.exports = {
+  initializeTransporter,
+  startEmailQueueProcessor,
   sendTemplateEmail,
   processEmailQueue,
   queueEmail,