Build a ChatGPT API Integrated Website with User Login, Stripe Payment & Admin Panel -- 2

We're looking for a fast and straightforward website that integrates with the ChatGPT API.

The website should feature:
• A dark, simple design inspired by Claude, ChatGPT or Grok, ensuring a modern and sleek look (the website purpose is therapy using ChatGPT)
• A fully responsive design optimized for mobile and desktop users
• A user login system with registration (login by username (email) and password / gmail / facebook) (when user register first time, he has to add Credit Card Number)
• Integration with Stripe for credit card processing, with a one-week free trial followed by monthly or yearly payments
• An admin panel to manage users and subscriptions and to see users ChatGPT threads
• Key Feature - Chat Functionality: The chat should support text and file upload, seamlessly integrating ChatGPT (our own model published on ChatGPT website) for real-time responses, ensuring a smooth user experience
• Website language: Czech, with preparation for additional languages in the future.

The project is expected to be completed within two weeks. Budget is open for proposals—please include a rough estimate in your bid.
Please include what frameworks would you use, I will need a cross platform mobile app in the future.

Chat specs:

New user, empty chat window:
- Headline
- short text
- buttons with two predefined questions for ChatGPT
- chat form

Returning user:
- the chat rememberes past text, the user continues like he didn't logout
- login other day: old text + buttons with predefined questions for ChatGPT