Web tests: add snapshot util coverage and vitest setup files

web/__test__/test-setup.ts

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+import "@testing-library/jest-dom";

web/__test__/testing-library.js

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+export * from "@testing-library/react";

web/src/utils/snapshotUtil.test.ts

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+import { describe, expect, it, vi } from "vitest";
+import {
+  downloadSnapshot,
+  generateSnapshotFilename,
+} from "@/utils/snapshotUtil";
+
+describe("generateSnapshotFilename", () => {
+  it("uses the provided playback timestamp in the filename", () => {
+    expect(generateSnapshotFilename("driveway", 1712592245, "UTC")).toBe(
+      "driveway_snapshot_2024-04-08T16-04-05.jpg",
+    );
+  });
+
+  it("uses the provided timezone so filename matches timeline-local time", () => {
+    expect(
+      generateSnapshotFilename("driveway", 1712592245, "America/Los_Angeles"),
+    ).toBe("driveway_snapshot_2024-04-08T09-04-05.jpg");
+  });
+
+  it("falls back to current time when no playback timestamp is provided", () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2024-08-09T10:11:12Z"));
+
+    expect(generateSnapshotFilename("front_yard", undefined, "UTC")).toBe(
+      "front_yard_snapshot_2024-08-09T10-11-12.jpg",
+    );
+
+    vi.useRealTimers();
+  });
+});
+
+describe("downloadSnapshot", () => {
+  it("creates and clicks a temporary anchor for download", () => {
+    const appendSpy = vi.spyOn(document.body, "appendChild");
+    const removeSpy = vi.spyOn(document.body, "removeChild");
+    const clickSpy = vi
+      .spyOn(HTMLAnchorElement.prototype, "click")
+      .mockImplementation(() => {});
+
+    downloadSnapshot("data:image/jpeg;base64,abc123", "snapshot.jpg");
+
+    expect(appendSpy).toHaveBeenCalledTimes(1);
+    expect(clickSpy).toHaveBeenCalledTimes(1);
+    expect(removeSpy).toHaveBeenCalledTimes(1);
+
+    const link = appendSpy.mock.calls[0]?.[0] as HTMLAnchorElement;
+    expect(link.download).toBe("snapshot.jpg");
+    expect(link.href).toContain("data:image/jpeg;base64,abc123");
+  });
+});