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/components/calendar/CalendarDay.test.tsx

@@ -0,0 +1,79 @@
+/**
+ * Unit tests for CalendarDay: click opens day detail only for current month;
+ * other-month cells do not call onDayClick and are non-interactive (aria-disabled).
+ */
+
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/react";
+import { CalendarDay } from "./CalendarDay";
+import { resetAppStore } from "@/test/test-utils";
+
+describe("CalendarDay", () => {
+  const defaultProps = {
+    dateKey: "2025-02-15",
+    dayOfMonth: 15,
+    isToday: false,
+    duties: [],
+    eventSummaries: [],
+    onDayClick: () => {},
+  };
+
+  beforeEach(() => {
+    resetAppStore();
+  });
+
+  it("calls onDayClick with dateKey and rect when clicked and isOtherMonth is false", () => {
+    const onDayClick = vi.fn();
+    render(
+      <CalendarDay
+        {...defaultProps}
+        isOtherMonth={false}
+        onDayClick={onDayClick}
+      />
+    );
+    const button = screen.getByRole("button", { name: /15/ });
+    fireEvent.click(button);
+
+    expect(onDayClick).toHaveBeenCalledTimes(1);
+    expect(onDayClick).toHaveBeenCalledWith(
+      "2025-02-15",
+      expect.objectContaining({
+        width: expect.any(Number),
+        height: expect.any(Number),
+        top: expect.any(Number),
+        left: expect.any(Number),
+      })
+    );
+  });
+
+  it("does not call onDayClick when clicked and isOtherMonth is true", () => {
+    const onDayClick = vi.fn();
+    render(
+      <CalendarDay
+        {...defaultProps}
+        isOtherMonth={true}
+        onDayClick={onDayClick}
+      />
+    );
+    const button = screen.getByRole("button", { name: /15/ });
+    fireEvent.click(button);
+
+    expect(onDayClick).not.toHaveBeenCalled();
+  });
+
+  it("sets aria-disabled on the button when isOtherMonth is true", () => {
+    render(
+      <CalendarDay {...defaultProps} isOtherMonth={true} onDayClick={() => {}} />
+    );
+    const button = screen.getByRole("button", { name: /15/ });
+    expect(button).toHaveAttribute("aria-disabled", "true");
+  });
+
+  it("is not disabled for interaction when isOtherMonth is false", () => {
+    render(
+      <CalendarDay {...defaultProps} isOtherMonth={false} onDayClick={() => {}} />
+    );
+    const button = screen.getByRole("button", { name: /15/ });
+    expect(button.getAttribute("aria-disabled")).not.toBe("true");
+  });
+});