Add deep-check e2e coverage

Verified via real HTTP path (not just the direct SSH test done while
building it): correctly identified Home Assistant via SSDP, 400 on
malformed IP, 401 unauthenticated, clean empty result for a device
with nothing to find (Echo-type devices deliberately minimize their
LAN footprint -- expected, not a bug).

Fixed the same substring-matching mistake caught earlier in
device-labeling.spec.ts, this time on "known" being a substring of
"unknown" -- switched to matching .device-badge.known specifically.

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

e2e/tests/deep-check.spec.ts

@@ -0,0 +1,47 @@
+import { test, expect } from "@playwright/test";
+
+const USERNAME = process.env.LOCAL_USERNAME ?? "admin";
+const PASSWORD = process.env.LOCAL_PASSWORD ?? "";
+
+test("deep check button runs a check and shows results for an unknown device", async ({ page }) => {
+  test.skip(!PASSWORD, "LOCAL_PASSWORD not set");
+
+  await page.goto("/");
+  await page.getByPlaceholder("Username").fill(USERNAME);
+  await page.getByPlaceholder("Password").fill(PASSWORD);
+  await page.getByRole("button", { name: "Sign in" }).click();
+  await expect(page.locator(".device-table tbody tr").first()).toBeVisible({ timeout: 15_000 });
+
+  const unknownRow = page.locator(".device-table tbody tr").filter({ hasText: "unknown" }).first();
+  await expect(unknownRow).toBeVisible();
+
+  const button = unknownRow.getByRole("button", { name: /deep check|checking/i });
+  await expect(button).toBeVisible();
+  await button.click();
+
+  await expect(button).toHaveText("Checking…");
+  // Bounded by the script's own timeouts (well under 15s) plus SSH round trip.
+  await expect(page.locator(".deep-check-row").first()).toBeVisible({ timeout: 20_000 });
+  await expect(button).toHaveText("Deep check");
+
+  // Either real findings (SSDP/mDNS/ports) or the explicit "nothing found"
+  // message -- either way, a result panel with actual content, not empty.
+  const resultRow = page.locator(".deep-check-row").first();
+  await expect(resultRow).not.toBeEmpty();
+});
+
+test("known devices have no deep check button", async ({ page }) => {
+  test.skip(!PASSWORD, "LOCAL_PASSWORD not set");
+
+  await page.goto("/");
+  await page.getByPlaceholder("Username").fill(USERNAME);
+  await page.getByPlaceholder("Password").fill(PASSWORD);
+  await page.getByRole("button", { name: "Sign in" }).click();
+  await expect(page.locator(".device-table tbody tr").first()).toBeVisible({ timeout: 15_000 });
+
+  // .device-badge.known specifically -- "known" is a substring of "unknown",
+  // so a text-based filter would match both (bit me on the labeling test too).
+  const knownRow = page.locator(".device-table tbody tr").filter({ has: page.locator(".device-badge.known") }).first();
+  await expect(knownRow).toBeVisible();
+  await expect(knownRow.getByRole("button", { name: /deep check/i })).toHaveCount(0);
+});