Fix router

In cleaning up the deps, for whatever reason, NPM started using react-router-dom's v6 types (instead of v5) for polycentric-react, which caused me to have to remove the "exact" param for path matching, making every page match with "/" and breaking navigation. This came from harbor relying on v6. Since harbor can easily be changed to use v5, until I finish removing all react-router-dom dependencies (all we use right now really is some nice path utility functions), this just downgrades harbor's router and re-adds the "exact" param.