test(e2e): cover the two guard-surface gaps found in the full-suite audit

Audit of all 12 e2e specs for the 'green-but-vacuous' class that broke
Grafana's SSO. The suite is otherwise sound (incident-driven, leakage-based);
two real coverage gaps surfaced:

- notebook.franksdank.cloud (open-notebook, deployed 2026-10-19) was a guarded
  vhost in NEITHER the 13-/14- GUARDED lists NOR any dedicated spec. A broken
  upstream would stay invisible - the exact 17-hermes class. Added to the 14-
  guard audit (unauth -> authentik gate, 'Open Notebook' leak marker) plus a
  new 21- that proves authenticated reachability to open-notebook's own login
  through the guard chain, with a positive app marker.
- prometheus.franksdank.cloud was only ever asserted '<500 and not a login
  wall' (13-/11-), which a 404 also passes. New 22- adds the app-is-really-
  there proof 20- gives Grafana: SSO handoff + its own /api/v1/status/buildinfo
  answers {status:success}.

Both specs wired into the standard project (playwright testMatch), which the
e2e_scaffold bats gate enforces. Verified live against the fleet; full bats
suite green.

tests/e2e/specs/21-notebook.spec.ts

@@ -0,0 +1,52 @@
+import { expect, test } from "@playwright/test";
+
+// open-notebook (notebook.franksdank.cloud), deployed 2026-10-19, is a guarded
+// vhost whose outpost (notebook-proxy) fronts an app with its OWN password
+// login - the same shape as hermes (17-) and OpenWebUI (18-): the guard chain
+// (Anubis PoW -> authentik outpost) must hand off to the app, and the app's own
+// login page is the expected landing. Until now this host appeared in neither
+// the 13-/14- GUARDED lists nor any dedicated spec, so a broken upstream would
+// have stayed invisible - the exact 17-hermes "uncovered vhost" failure class.
+// 14- now covers the unauthenticated gate; this spec owns authenticated
+// reachability with a POSITIVE app marker, not just "not a login wall".
+
+const VHOST = "https://notebook.franksdank.cloud/";
+const CHALLENGE = "Making sure you're not a bot";
+
+test("notebook vhost reaches the open-notebook app through the guard chain", async ({ page }) => {
+  test.setTimeout(180_000);
+  await page.goto(VHOST);
+
+  // The Anubis proof-of-work clears in a real browser and the outpost hands off
+  // to the app; the user must never be parked on an authentik flow.
+  await expect
+    .poll(async () => !(await page.locator("body").innerText()).includes(CHALLENGE), { timeout: 90_000 })
+    .toBe(true);
+  await expect
+    .poll(() => new URL(page.url()).hostname, { timeout: 60_000 })
+    .toBe("notebook.franksdank.cloud");
+  expect(
+    new URL(page.url()).pathname.startsWith("/if/"),
+    "must not be parked on an authentik flow",
+  ).toBe(false);
+  expect(
+    await page.locator('input[name="uidField"]').count(),
+    "must not show the authentik login form",
+  ).toBe(0);
+
+  // Positive identity: the page really is open-notebook's own login, not a
+  // Caddy error or the IdP shell. The app answering its own login is the pass.
+  await expect(page, "destination title must be Open Notebook").toHaveTitle(/open notebook/i, {
+    timeout: 30_000,
+  });
+  await expect(page.locator("body"), "open-notebook login marker").toContainText(
+    /enter your password/i,
+    { timeout: 30_000 },
+  );
+  const body = await page.locator("body").innerText();
+  expect(body, "must not leak the IdP flow shell").not.toContain("Powered by authentik");
+  expect(body, "must not be a Caddy upstream error").not.toContain("Bad Gateway");
+
+  const resp = await page.request.get(VHOST);
+  expect(resp.status(), "open-notebook must answer, not error").toBeLessThan(500);
+});