Add frontend tests (#22783)

* basic e2e frontend test framework

* improve mock data generation and add test cases

* more cases

* add e2e tests to PR template

* don't generate mock data in PR CI

* satisfy codeql check

* fix flaky system page tab tests by guarding against crashes from incomplete mock stats

* reduce local test runs to 4 workers to match CI

web/e2e/specs/face-library.spec.ts

@@ -0,0 +1,32 @@
+/**
+ * Face Library page tests -- MEDIUM tier.
+ *
+ * Tests face grid rendering, empty state, and interactive controls.
+ */
+
+import { test, expect } from "../fixtures/frigate-test";
+
+test.describe("Face Library @medium", () => {
+  test("face library page renders without crash", async ({ frigateApp }) => {
+    await frigateApp.goto("/faces");
+    await expect(frigateApp.page.locator("#pageRoot")).toBeVisible();
+  });
+
+  test("face library shows empty state with no faces", async ({
+    frigateApp,
+  }) => {
+    await frigateApp.goto("/faces");
+    await frigateApp.page.waitForTimeout(2000);
+    // With empty faces mock, should show empty state or content
+    const text = await frigateApp.page.textContent("#pageRoot");
+    expect(text?.length).toBeGreaterThan(0);
+  });
+
+  test("face library has interactive buttons", async ({ frigateApp }) => {
+    await frigateApp.goto("/faces");
+    await frigateApp.page.waitForTimeout(2000);
+    const buttons = frigateApp.page.locator("#pageRoot button");
+    const count = await buttons.count();
+    expect(count).toBeGreaterThanOrEqual(0);
+  });
+});