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/types/index.ts

@@ -0,0 +1,25 @@
+/**
+ * TypeScript types for API responses and calendar data.
+ * Mirrors duty_teller/db/schemas.py (DutyWithUser, CalendarEvent).
+ */
+
+/** Duty event type returned by the API; unknown DB values are mapped to "duty". */
+export type DutyEventType = "duty" | "unavailable" | "vacation";
+
+/** Duty with user and contact fields for calendar display (UTC ISO 8601). */
+export interface DutyWithUser {
+  id: number;
+  user_id: number;
+  start_at: string;
+  end_at: string;
+  full_name: string;
+  event_type: DutyEventType;
+  phone: string | null;
+  username: string | null;
+}
+
+/** External calendar event (e.g. holiday) for a single day (YYYY-MM-DD). */
+export interface CalendarEvent {
+  date: string;
+  summary: string;
+}