Improve backend security, reliability, testing, and task management

[RobotEby]

Description

This PR improves the application’s security, organization, and reliability, while also expanding task management and quality automation.

Backend

• Removes the hardcoded JWT secret and centralizes configuration via environment variables.
• Refactors the monolithic backend into a layered architecture.
• Adds input validation and centralized error handling.
• Adds support for due dates and persistent task ordering.
• Implements health check endpoints for the API and MongoDB.
• Adds unit and integration tests using Jest and Supertest.

Frontend

• Persists task ordering in the backend.
• Restores the previous order when persistence fails.
• Corrects the execution order of hooks on the main page.
• Localizes the loading message for the protected route.
• Adds static validation with lint and TypeScript.

Docker and Infrastructure

• Adds health checks for the backend and MongoDB.
• Waits for the database to be healthy before starting the API.
• Enables test execution via Docker Compose.
• Replaces the backend dependency installation with npm ci.

CI and Documentation

• Adds a workflow for linting, testing, type checking, frontend building, and Docker image validation.
• Updates the README with instructions for running the application, testing, API reference, security, and known limitations.

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Project	Deployment	Actions	Updated (UTC)
docker-todo-list	Ready	Preview	Aug 28, 2026 9:59pm