Add Fingerbank e2e coverage; fix two test races found along the way

- deep-check.spec.ts: new test asserting a Fingerbank ID + confidence
  label appears (targets the Nintendo device specifically, skips if
  it's not currently on the network -- not something the test suite
  controls). First run false-skipped because it checked row.count()
  before waiting for the device table to actually render.
- device-ratio.spec.ts: badge counts and displayed text were read as
  two separate one-shot queries (.count()/.textContent() don't
  auto-retry like expect() matchers), which raced a background poll
  once and failed. Wrapped the whole comparison in expect().toPass()
  so it retries atomically instead. Confirmed fixed: 4/4 clean runs
  with retries disabled.

15/15 e2e tests green across 8 spec files.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

e2e/tests/device-ratio.spec.ts

@@ -12,12 +12,17 @@ test("known/unknown ratio matches the actual badge counts", async ({ page }) =>
   await page.getByRole("button", { name: "Sign in" }).click();
   await expect(page.locator(".device-table tbody tr").first()).toBeVisible({ timeout: 15_000 });
 
-  const knownCount = await page.locator(".device-badge.known").count();
-  const unknownCount = await page.locator(".device-badge.unknown").count();
-
-  const ratioText = await page.locator(".device-ratio").textContent();
-  expect(ratioText).toBe(`${knownCount} known / ${unknownCount} unknown`);
-
-  const countText = await page.locator(".device-count").textContent();
-  expect(countText).toBe(`(${knownCount + unknownCount})`);
+  // Re-reads badge counts and the displayed text together, retrying the
+  // whole comparison if they're ever caught mid-render (e.g. a background
+  // poll landing between the two reads) instead of a one-shot comparison —
+  // .count() and .textContent() don't auto-wait/retry the way expect()
+  // matchers do, so a bare single read raced a poll and failed once already.
+  await expect(async () => {
+    const knownCount = await page.locator(".device-badge.known").count();
+    const unknownCount = await page.locator(".device-badge.unknown").count();
+    const ratioText = await page.locator(".device-ratio").textContent();
+    const countText = await page.locator(".device-count").textContent();
+    expect(ratioText).toBe(`${knownCount} known / ${unknownCount} unknown`);
+    expect(countText).toBe(`(${knownCount + unknownCount})`);
+  }).toPass({ timeout: 10_000 });
 });