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/store/app-store.ts

@@ -0,0 +1,85 @@
+/**
+ * Global application state (Zustand).
+ * Replaces the mutable state from webapp/js/dom.js.
+ */
+
+import { create } from "zustand";
+import type { DutyWithUser, CalendarEvent } from "@/types";
+import { getStartParamFromUrl } from "@/lib/launch-params";
+
+export type CurrentView = "calendar" | "currentDuty";
+
+export interface AppState {
+  currentMonth: Date;
+  lang: "ru" | "en";
+  duties: DutyWithUser[];
+  calendarEvents: CalendarEvent[];
+  loading: boolean;
+  error: string | null;
+  accessDenied: boolean;
+  /** Server detail from API 403 response; shown in AccessDenied component. */
+  accessDeniedDetail: string | null;
+  currentView: CurrentView;
+  selectedDay: string | null;
+
+  setCurrentMonth: (d: Date) => void;
+  nextMonth: () => void;
+  prevMonth: () => void;
+  setDuties: (d: DutyWithUser[]) => void;
+  setCalendarEvents: (e: CalendarEvent[]) => void;
+  setLoading: (v: boolean) => void;
+  setError: (msg: string | null) => void;
+  setAccessDenied: (v: boolean) => void;
+  setAccessDeniedDetail: (v: string | null) => void;
+  setLang: (v: "ru" | "en") => void;
+  setCurrentView: (v: CurrentView) => void;
+  setSelectedDay: (key: string | null) => void;
+  /** Batch multiple state updates into a single re-render. */
+  batchUpdate: (partial: Partial<Pick<AppState, "currentMonth" | "lang" | "duties" | "calendarEvents" | "loading" | "error" | "accessDenied" | "accessDeniedDetail" | "currentView" | "selectedDay">>) => void;
+}
+
+const now = new Date();
+const initialMonth = new Date(now.getFullYear(), now.getMonth(), 1);
+
+/** Initial view: currentDuty when opened via deep link (startParam=duty), else calendar. */
+function getInitialView(): CurrentView {
+  if (typeof window === "undefined") return "calendar";
+  return getStartParamFromUrl() === "duty" ? "currentDuty" : "calendar";
+}
+
+export const useAppStore = create<AppState>((set) => ({
+  currentMonth: initialMonth,
+  lang: "en",
+  duties: [],
+  calendarEvents: [],
+  loading: false,
+  error: null,
+  accessDenied: false,
+  accessDeniedDetail: null,
+  currentView: getInitialView(),
+  selectedDay: null,
+
+  setCurrentMonth: (d) => set({ currentMonth: d }),
+  nextMonth: () =>
+    set((s) => {
+      const next = new Date(s.currentMonth);
+      next.setMonth(next.getMonth() + 1);
+      return { currentMonth: next };
+    }),
+  prevMonth: () =>
+    set((s) => {
+      const prev = new Date(s.currentMonth);
+      prev.setMonth(prev.getMonth() - 1);
+      return { currentMonth: prev };
+    }),
+  setDuties: (d) => set({ duties: d }),
+  setCalendarEvents: (e) => set({ calendarEvents: e }),
+  setLoading: (v) => set({ loading: v }),
+  setError: (msg) => set({ error: msg }),
+  setAccessDenied: (v) => set({ accessDenied: v }),
+  setAccessDeniedDetail: (v) => set({ accessDeniedDetail: v }),
+  setLang: (v) => set({ lang: v }),
+  setCurrentView: (v) => set({ currentView: v }),
+  setSelectedDay: (key) => set({ selectedDay: key }),
+  batchUpdate: (partial) => set(partial),
+}));