chore: make vite dev server port configurable

[mas-who]

Done

• Make vite dev server port configurable. It is set to 3000 by default so we don't need to worry about creating an extra secret for the demo environment.
• Added to the docs about configuring VITE_PORT

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @mas-who or @edlerd for access.
   • With a local copy of this branch, build and run as described in the docs.
2. Perform the following QA steps:
   • Ensure CI passes
   • Check starting the local dev environment and the UI loads
   • Check the demo server and make sure UI loads

[webteam-app]

Demo

Jenkins

demos.haus

[lorumic]

Looks good, just a couple of minor ideas :)