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/test/setup.ts

@@ -0,0 +1,17 @@
+import "@testing-library/jest-dom/vitest";
+import { vi } from "vitest";
+
+// jsdom does not provide window.matchMedia (used by use-media-query and use-telegram-theme).
+Object.defineProperty(window, "matchMedia", {
+  writable: true,
+  value: vi.fn().mockImplementation((query: string) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});

webapp-next/src/test/test-utils.tsx

@@ -0,0 +1,34 @@
+/**
+ * Test utilities: custom render with app store and optional providers.
+ */
+
+import React, { ReactElement } from "react";
+import { render, RenderOptions } from "@testing-library/react";
+import { useAppStore } from "@/store/app-store";
+
+/** Reset app store to a known state before tests that need it. */
+export function resetAppStore() {
+  const state = useAppStore.getState();
+  state.setLang("en");
+  state.setCurrentMonth(new Date(2025, 0, 1)); // Feb 2025
+  state.setDuties([]);
+  state.setCalendarEvents([]);
+  state.setLoading(false);
+  state.setError(null);
+  state.setAccessDenied(false);
+  state.setCurrentView("calendar");
+  state.setSelectedDay(null);
+}
+
+function AllTheProviders({ children }: { children: React.ReactNode }) {
+  return <>{children}</>;
+}
+
+function customRender(ui: ReactElement, options?: Omit<RenderOptions, "wrapper">) {
+  return render(ui, {
+    wrapper: AllTheProviders,
+    ...options,
+  });
+}
+
+export { customRender as render };