Migrate from current version of node to the latest (23)

[Dr-Agentic]

The project currently uses Node.js v18 (as defined in backend/Dockerfile). We need to upgrade the project to use the latest Node.js version (v23).

Tasks:

• Update backend/Dockerfile to use node:23-alpine.
• Add/Update engines field in package.json to specify node: ">=23".
• Update @types/node in package.json to the latest version.
• Verify build pipelines and tests.