Add user prefs, update capsule to always exist, fix lifetime bug somehow

src/endpoints.rs

@@ -1,5 +1,6 @@
 pub const REGISTER: &str = "/api/register";
 pub const LOGIN: &str = "/api/login";
+pub const UPDATE_USER_PREFS: &str = "/api/user-prefs";
 // TODO -> remove once it's used
 #[cfg(engine)]
 pub const LOGIN_TEST: &str = "/api/login-test";