Prepare application for production deployment with Docker and PostgreSQL

Integrate PostgreSQL database support, add Docker deployment configurations, and implement health check endpoints.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ceced2fc-aa46-458d-ba87-ddd4b7bb1518
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/659922a9-0087-461c-90dd-6d9a58b81d4d/ceced2fc-aa46-458d-ba87-ddd4b7bb1518/ahHWEFX

.env.example

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+# Application Configuration
+NODE_ENV=production
+PORT=5000
+
+# Database Configuration (Docker Compose)
+# These are used by docker-compose.yml to create the PostgreSQL container
+POSTGRES_USER=taskflow
+POSTGRES_PASSWORD=taskflow_password
+POSTGRES_DB=taskflow
+POSTGRES_PORT=5432
+
+# Database URL (used by the application)
+# Format: postgresql://user:password@host:port/database
+# For Docker: use the service name 'postgres' as the host
+DATABASE_URL=postgresql://taskflow:taskflow_password@postgres:5432/taskflow
+
+# For external PostgreSQL (non-Docker):
+# DATABASE_URL=postgresql://user:password@your-db-host:5432/your-db-name
+
+# Application Port (external mapping)
+APP_PORT=5000
+
+# Development Mode (optional)
+# Set USE_DB=true to use database in development mode
+# USE_DB=true