Make HTTP port and CORS origin environment-configurable

[CryptoJones]

Problem

server.js hardcodes two production-blocking values:

• Listen port 80 — requires root or a setcap to run, blocking npm start for non-privileged users and most containers.
• CORS origin http://localhost:4200 — unusable in any real deployment without editing the file.

Scope

• Read the listen port from process.env.PORT with a sensible default (e.g., 3000).
• Read the CORS origin from process.env.CORS_ORIGIN, accepting a single origin or a comma-separated list. Document a safe default.
• Add an Environment Variables section to README.md and ship a .env.example.

Acceptance criteria

• PORT=3000 npm start works for a non-root user.
• CORS_ORIGIN=https://example.com node server.js enforces that origin only.
• README has an Environment Variables table.
• .env.example is committed with placeholder values.

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