feat: migrate to Next.js for Mini App and enhance project structure

- Replaced the previous webapp with a new Mini App built using Next.js, improving performance and maintainability.
- Updated the `.gitignore` to exclude Next.js build artifacts and node modules.
- Revised documentation in `AGENTS.md`, `README.md`, and `architecture.md` to reflect the new Mini App structure and technology stack.
- Enhanced Dockerfile to support the new build process for the Next.js application.
- Updated CI workflow to build and test the Next.js application.
- Added new configuration options for the Mini App, including `MINI_APP_SHORT_NAME` for improved deep linking.
- Refactored frontend testing setup to accommodate the new structure and testing framework.
- Removed legacy webapp files and dependencies to streamline the project.

webapp-next/src/lib/constants.ts

@@ -0,0 +1,9 @@
+/**
+ * Application constants for API and retry behaviour.
+ */
+
+export const FETCH_TIMEOUT_MS = 15000;
+export const RETRY_DELAY_MS = 800;
+export const RETRY_AFTER_ACCESS_DENIED_MS = 1200;
+export const RETRY_AFTER_ERROR_MS = 800;
+export const MAX_GENERAL_RETRIES = 2;