feat: implement relative date formatting, real-time clock display

frontend/src/utils/dateFormat.test.ts

@@ -0,0 +1,37 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { formatRelativeDate } from "./dateFormat";
+
+describe("formatRelativeDate", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-04-14T15:30:00Z"));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("should format a same-day timestamp as Today, <time>", () => {
+    const result = formatRelativeDate("2026-04-14T10:15:00Z");
+
+    expect(result).toBe("Today, 3:45 PM");
+  });
+
+  it("should format a previous-day timestamp as Yesterday, <time>", () => {
+    const result = formatRelativeDate("2026-04-13T09:10:00Z");
+
+    expect(result).toBe("Yesterday, 2:40 PM");
+  });
+
+  it("should format dates within the last week as relative day + time", () => {
+    const result = formatRelativeDate("2026-04-12T08:00:00Z");
+
+    expect(result).toBe("2 days ago, 1:30 PM");
+  });
+
+  it("should format dates older than a week as a full date+time", () => {
+    const result = formatRelativeDate("2026-04-01T13:15:00Z");
+
+    expect(result).toBe("Apr 1, 2026, 6:45 PM");
+  });
+});