I agree with the other answers that recommend Java, especially as you may need it's speed in the AI code, and for the libraries etc. that are available.
A combination of Java (servlets) and JSP would probably work nicely.
However, the reason for writing this answer is to most highly recommend:
Go with what you know.
New languages or ones you "sort of" know are great for fun stuff, and even for some development projects and prototyping. But if you need something that will work for you in the long run, use the best language for the task THAT YOU ALREADY KNOW. In this case, I think (from your post) it would be Java.
Also - it's a prototype now, but I can almost guarantee that if it works, it will become the default start of the actual application. I really doubt you will have the luxury of time to rewrite the application from scratch in another language, so again - using what you know now will pay dividends later when they "time crunch" you and you must deliver.
Cheers,
-R