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/app/build.rs

@@ -120,7 +120,12 @@ fn main() {
             .plugin(
                 "mr-auth",
                 InlinedPlugin::new()
-                    .commands(&["modrinth_login", "logout", "get"])
+                    .commands(&[
+                        "modrinth_login",
+                        "logout",
+                        "get",
+                        "cancel_modrinth_login",
+                    ])
                     .default_permission(
                         DefaultPermissionRule::AllowAllCommands,
                     ),