test(e2e): Playwright UI smoke + Go integration tests against MAS

- Playwright e2e against Vite dev server (LoginScreen renders, homeserver
  visible, version pinned). Fallback documented to swap to `wails dev
  -browser` via WAILS_DEV_URL when full backend bindings are required.
- Go integration tests (//go:build integration,goolm) for Start +
  ListRooms + LoadTimeline + SendText + GetDiagnostics against real
  Synapse. Skip cleanly if MATRIX_INTEGRATION_TOKEN/USER env vars unset
  so CI never breaks unattended.
- pnpm e2e/e2e:ui/e2e:report scripts. Per-run keyring namespace +
  t.TempDir XDG_CONFIG_HOME so integration tests don't clobber the
  production keyring entry.

E2E.md explains how to run each layer + limits (OIDC not automated).

frontend/e2e/login_screen.spec.ts

@@ -0,0 +1,33 @@
+import { test, expect } from "@playwright/test";
+
+// UI smoke against the React frontend served by Vite. We don't need a real
+// Wails backend: the only runtime call on mount (GetLastUserID) throws because
+// window.go is undefined, the catch path drops the loading overlay, and
+// LoginScreen renders identically to what the production app shows on first
+// launch. This catches HTML/CSS/asset regressions + Mantine bundle errors
+// without dragging the full Go+goolm compile into CI.
+
+test("LoginScreen renders with Sign-in button", async ({ page }) => {
+  // Swallow uncaught Wails-runtime errors so they don't fail the test.
+  page.on("pageerror", () => {});
+  await page.goto("/");
+  await expect(page.getByRole("heading", { name: /matrix_client_pc/i })).toBeVisible();
+  await expect(
+    page.getByRole("button", { name: /sign in with matrix/i }),
+  ).toBeVisible();
+});
+
+test("LoginScreen mentions homeserver + MAS context", async ({ page }) => {
+  page.on("pageerror", () => {});
+  await page.goto("/");
+  await expect(page.getByText(/matrix-af2f3d/)).toBeVisible();
+  await expect(
+    page.getByText(/matrix authentication service/i),
+  ).toBeVisible();
+});
+
+test("LoginScreen shows version tag", async ({ page }) => {
+  page.on("pageerror", () => {});
+  await page.goto("/");
+  await expect(page.getByText(/v0\.1\.0 \(issue 0147\)/i)).toBeVisible();
+});