fix(CQ-WEB-10): Add loading/error states to pages with mock data

Convert tasks, calendar, and dashboard pages from synchronous mock data
to async loading pattern with useState/useEffect. Each page now shows a
loading state via child components while data loads, and displays a
PDA-friendly amber-styled message with a retry button if loading fails.

This prepares these pages for real API integration by establishing the
async data flow pattern. Child components (TaskList, Calendar, dashboard
widgets) already handled isLoading props — now the pages actually use them.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/app/(authenticated)/calendar/page.test.tsx

@@ -0,0 +1,46 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import CalendarPage from "./page";
+
+// Mock the Calendar component
+vi.mock("@/components/calendar/Calendar", () => ({
+  Calendar: ({
+    events,
+    isLoading,
+  }: {
+    events: unknown[];
+    isLoading: boolean;
+  }): React.JSX.Element => (
+    <div data-testid="calendar">{isLoading ? "Loading" : `${String(events.length)} events`}</div>
+  ),
+}));
+
+describe("CalendarPage", (): void => {
+  it("should render the page title", (): void => {
+    render(<CalendarPage />);
+    expect(screen.getByRole("heading", { level: 1 })).toHaveTextContent("Calendar");
+  });
+
+  it("should show loading state initially", (): void => {
+    render(<CalendarPage />);
+    expect(screen.getByTestId("calendar")).toHaveTextContent("Loading");
+  });
+
+  it("should render the Calendar with events after loading", async (): Promise<void> => {
+    render(<CalendarPage />);
+    await waitFor((): void => {
+      expect(screen.getByTestId("calendar")).toHaveTextContent("3 events");
+    });
+  });
+
+  it("should have proper layout structure", (): void => {
+    const { container } = render(<CalendarPage />);
+    const main = container.querySelector("main");
+    expect(main).toBeInTheDocument();
+  });
+
+  it("should render the subtitle text", (): void => {
+    render(<CalendarPage />);
+    expect(screen.getByText("View your schedule at a glance")).toBeInTheDocument();
+  });
+});

apps/web/src/app/(authenticated)/calendar/page.tsx

@@ -1,18 +1,39 @@
 "use client";
 
+import { useState, useEffect } from "react";
 import type { ReactElement } from "react";
 import { Calendar } from "@/components/calendar/Calendar";
 import { mockEvents } from "@/lib/api/events";
+import type { Event } from "@mosaic/shared";
 
 export default function CalendarPage(): ReactElement {
-  // TODO: Replace with real API call when backend is ready
-  // const { data: events, isLoading } = useQuery({
-  //   queryKey: ["events"],
-  //   queryFn: fetchEvents,
-  // });
+  const [events, setEvents] = useState<Event[]>([]);
+  const [isLoading, setIsLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
 
-  const events = mockEvents;
-  const isLoading = false;
+  useEffect(() => {
+    void loadEvents();
+  }, []);
+
+  async function loadEvents(): Promise<void> {
+    setIsLoading(true);
+    setError(null);
+
+    try {
+      // TODO: Replace with real API call when backend is ready
+      // const data = await fetchEvents();
+      await new Promise((resolve) => setTimeout(resolve, 300));
+      setEvents(mockEvents);
+    } catch (err) {
+      setError(
+        err instanceof Error
+          ? err.message
+          : "We had trouble loading your calendar. Please try again when you're ready."
+      );
+    } finally {
+      setIsLoading(false);
+    }
+  }
 
   return (
     <main className="container mx-auto px-4 py-8">
@@ -20,7 +41,20 @@ export default function CalendarPage(): ReactElement {
         <h1 className="text-3xl font-bold text-gray-900">Calendar</h1>
         <p className="text-gray-600 mt-2">View your schedule at a glance</p>
       </div>
-      <Calendar events={events} isLoading={isLoading} />
+
+      {error !== null ? (
+        <div className="rounded-lg border border-amber-200 bg-amber-50 p-6 text-center">
+          <p className="text-amber-800">{error}</p>
+          <button
+            onClick={() => void loadEvents()}
+            className="mt-4 rounded-md bg-amber-600 px-4 py-2 text-sm font-medium text-white hover:bg-amber-700 transition-colors"
+          >
+            Try again
+          </button>
+        </div>
+      ) : (
+        <Calendar events={events} isLoading={isLoading} />
+      )}
     </main>
   );
 }