Improve frontend test framework (#22824)

* add error allowlist file for error collector

* add error collector for console + page + request errors

* wire error collector into frigateApp fixture

* add self-tests for error collector fixture

* gate strict error mode on E2E_STRICT_ERRORS=1

* triage pre-existing errors and seed allowlist

* add mockEmpty/mockError/mockDelay helpers for state-driven tests

* add self-tests for mock override helpers

* add mobile affordance helpers to BasePage

* add lint script for banned spec patterns and @mobile rule

* apply prettier fixes to new e2e files

* rewrite export.spec.ts

* clean up

* move export spec rewrite and bugfix to separate branch

web/e2e/helpers/mock-overrides.ts

@@ -0,0 +1,56 @@
+/**
+ * Per-test mock overrides for driving empty / loading / error states.
+ *
+ * Playwright route handlers are LIFO: the most recently registered handler
+ * matching a URL takes precedence. The frigateApp fixture installs default
+ * mocks before the test body runs, so these helpers — called inside the
+ * test body — register AFTER the defaults and therefore win.
+ *
+ * Always call these BEFORE the navigation that triggers the request.
+ *
+ * Example:
+ *   await mockEmpty(page, "**\/api\/exports**");
+ *   await frigateApp.goto("/export");
+ *   // Page now renders the empty state
+ */
+
+import type { Page } from "@playwright/test";
+
+/** Return an empty array for the matched endpoint. */
+export async function mockEmpty(
+  page: Page,
+  urlPattern: string | RegExp,
+): Promise<void> {
+  await page.route(urlPattern, (route) => route.fulfill({ json: [] }));
+}
+
+/** Return an HTTP error for the matched endpoint. Default status 500. */
+export async function mockError(
+  page: Page,
+  urlPattern: string | RegExp,
+  status = 500,
+): Promise<void> {
+  await page.route(urlPattern, (route) =>
+    route.fulfill({
+      status,
+      json: { success: false, message: "Mocked error" },
+    }),
+  );
+}
+
+/**
+ * Delay the response by `ms` milliseconds before fulfilling with the
+ * provided body. Use to assert loading-state UI is visible during the
+ * delay window.
+ */
+export async function mockDelay(
+  page: Page,
+  urlPattern: string | RegExp,
+  ms: number,
+  body: unknown = [],
+): Promise<void> {
+  await page.route(urlPattern, async (route) => {
+    await new Promise((resolve) => setTimeout(resolve, ms));
+    await route.fulfill({ json: body });
+  });
+}