fix: allow dynamic server port via environment variable

[giuliolibrando]

Replaced hardcoded port 3000 with process.env.PORT in src/index.tsx to support custom deployment environments.

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Summary by cubic

Server now reads the port from process.env.PORT, falling back to 3000. This enables deployments on platforms that assign dynamic ports.

^{Written for commit b08bcca. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

[C4illin]

When would you need this in a deployment?

[giuliolibrando]

Cause I used the proxmox script helper ( https://community-scripts.github.io/ProxmoxVE/scripts?id=convertx ) and I was not able to change the port to 80. It doesn't use docker, I would have had to expose the traffic via nginx proxy manager but this way less pieces are needed. Why hardcode the port?