Subscription and payment

• Integrate Yookassa api
• Set up backend structure for subscription plans
• Handle success/failure payment callbacks

📋 Acceptance Criteria

✅ What to consider:

• The system must integrate seamlessly with the Telegram Payments API to support in-chat transactions.
• Subscription plans must be clearly defined and handled through a structured backend system.
• Both successful and failed payments should trigger appropriate system behavior and user feedback (via callback handling).

✅ Acceptance Criteria (AC):

• GIVEN a user opens the payment screen in Telegram

• WHEN they proceed to pay for a subscription

• THEN the payment is processed using the Yookassa api

• GIVEN the backend is initialized

• WHEN a user selects a plan

• THEN the correct plan data is retrieved and stored based on their choice

• GIVEN a payment transaction completes

• WHEN it succeeds

• THEN the user gains access to the selected plan, and a confirmation message is sent

• GIVEN a payment transaction fails

• WHEN the callback is received

• THEN the system logs the failure and notifies the user with a retry or support message

✅ Please check the Definition of Done before moving this issue to Close.