feat(app): better external browser Modrinth login flow (#4033)

* fix(app-frontend): do not emit exceptions when no loaders are available

* refactor(app): simplify Microsoft login code without functional changes

* feat(app): external browser auth flow for Modrinth account login

* chore: address Clippy lint

* chore(app/oauth_utils): simplify `handle_reply` error handling according to review

* chore(app-lib): simplify `Url` usage out of MC auth module

apps/frontend/src/pages/auth/sign-up.vue

@@ -247,16 +247,14 @@ async function createAccount() {
       },
     });
 
-    if (route.query.launcher) {
-      await navigateTo(`https://launcher-files.modrinth.com/?code=${res.session}`, {
-        external: true,
-      });
-      return;
-    }
-
     await useAuth(res.session);
     await useUser();
 
+    if (route.query.launcher) {
+      await navigateTo({ path: "/auth/sign-in", query: route.query });
+      return;
+    }
+
     if (route.query.redirect) {
       await navigateTo(route.query.redirect);
     } else {