TLDR: If AngularJS isn't working, invalidate the caches (File -> "Invalidate Caches / Restart") to force everything to be reloaded.
In case any one else is having this issue:
I just installed IDEA 13.1 overtop my 13.0 installation. When I restarted, I couldn't get AngularJS to work at all. There were no suggestions, ng-* attributes were marked invalid, etc. I was about to pull my hair out, because it was working in a different project, which was a fork of this one.
Anyway, the main difference I could see was that one had a space in the name, and the other didn't. I decided to rename the folder and see if that helped, which, magically it did. I renamed it back, to see if it was an issue with the plugin, but everything was still working.
I'm taking a small guess here, but I think it basically invalidated all the cache data for the project, and forced it to reload. If I'm right (and maybe someone can chime in here), then simply going to File, Invalidate Caches / Restart and invalidating the caches will probably fix your issue.