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).

.gitignore

@@ -23,3 +23,9 @@ local_files/
 # OS
 .DS_Store
 Thumbs.db
+
+# Playwright (E2E)
+frontend/playwright-report/
+frontend/test-results/
+frontend/blob-report/
+frontend/.playwright/