feat(frontend): reduce flickering on reload (#9897)

* rename states to better fit naming conv

* fix name

* ensure splashscreen only loads after login check
this reduces a short splash of the splashscreen even if logged in

* move loader to the middle of the screen and remove fallback on a view screens

src/frontend/lib/types/User.tsx

@@ -59,4 +59,7 @@ export interface UserStateProps {
   isLoggedIn: () => boolean;
   isStaff: () => boolean;
   isSuperuser: () => boolean;
+  // login state
+  login_checked: boolean;
+  setLoginChecked: (value: boolean) => void;
 }