LoginForm: restore proper <label> elements + update e2e tests to the single-step flow

The local-mode LoginForm had drifted to using styled <div> elements as
labels. That's an a11y regression — screen readers can't associate the
label text with the input, and it broke every e2e sign-in helper because
playwright's getByLabel needs a real <label htmlFor="…"> (or aria-label)
association. Restore proper <label htmlFor="email"|"password"> with
matching id="…" on the inputs; keeps the current design comp untouched.

The tests were also written for an OLDER two-step flow — enter email →
click "Continue with work email" → enter password → click "Sign in".
The current form is single-step (both fields, one Sign in click). Update
the shared signIn helper in every spec (p0-p8 + visual) to match, and
switch the label selector to "Email address" so it matches the newly
restored <label> text. Drop the stale a11y assertion in p6 that expected
the two-step button.

Also refresh the marketing landing check in p0-shell.spec.ts:20-22 —
"agentic systems" was in the H1 in an older copy pass; today's H1 is
"Deploy agents at any scale." Update the selector.

Together this unblocks ~30 of the 32 e2e failures; the remaining handful
are downstream product/test drift that will need per-test attention.

frontend/tests/e2e/p8-topology.spec.ts

@@ -8,8 +8,7 @@ const OWNER_PASSWORD = "e2e-password";
 
 async function signIn(page: Page) {
   await page.goto("/login");
-  await page.getByLabel("Email").fill(OWNER_EMAIL);
-  await page.getByRole("button", { name: /Continue with work email/ }).click();
+  await page.getByLabel("Email address").fill(OWNER_EMAIL);
   await page.getByLabel("Password").fill(OWNER_PASSWORD);
   await page.getByRole("button", { name: "Sign in" }).click();
   await expect(page.getByRole("heading", { name: "Clawmates" })).toBeVisible();