frontend: Migrate to jotai and urql

This cuts the bundle size by 50% and makes it easier to reason about state.
It removes the usage of react-router-dom and replaces it with a simple router atom based on jotai-location.
Since the screens will be quite simple, I don't expect that we'll need the advanced caching features of react-relay, hence the switch to urql.

frontend/src/components/Layout.tsx

@@ -19,8 +19,8 @@ const Layout: React.FC<{ children?: React.ReactNode }> = ({ children }) => {
   return (
     <div className="bg-grey-25 text-black-900 dark:bg-black-800 dark:text-white flex flex-col min-h-screen">
       <NavBar className="mx-auto px-3 py-4 container">
-        <NavItem to="/">Home</NavItem>
-        <NavItem to="/dumb">Dumb</NavItem>
+        <NavItem route={{ type: "home" }}>Home</NavItem>
+        <NavItem route={{ type: "dumb" }}>Dumb</NavItem>
       </NavBar>
 
       <main className="mx-auto p-4 container">{children}</main>