I already run https://casaspakw.com/ and have wrapped it in an Android WebView (built with WebIntoApp). The shell works, but it still feels like “a website in a browser.” I now need a true app experience. The first milestone is a secure authentication flow that lets people register and sign in with BOTH email-and-password and phone-number-plus-OTP. A user who creates an account inside the app must be able to use the same credentials on the website, and vice-versa. I’m undecided about adding social logins; please outline the extra effort and I’ll decide once I see the impact. You’re free to suggest the tech—Firebase Auth, a WordPress plugin that ties into my existing stack, or a lightweight custom backend—just explain why your choice is the best match. If you can bundle a simple appointment / booking module so customers can reserve spa treatments directly from the app, quote that as an optional add-on. UI expectations: • Minimal, clean screens for Sign-Up, Log-In, OTP Verification, Forgot Password, Profile (and Booking if included) • Consistent brand colours and typography • Smooth on every common Android resolution, plus responsive on mobile web When the features are ready, I’ll also need help preparing the signed bundle and pushing the update to Google Play. Please include in your reply: • Links to similar apps where you built email + phone login • The stack you propose and why • Estimated timeline with milestone breakdown and total cost My goal is a polished, professional Android experience, not just an embedded site.