Add forward auth E2E tests with Dex OIDC provider
- Add Dex OIDC provider to test Docker Compose stack with static test
users (alice, bob) and pre-configured OAuth client
- Add forward-auth.spec.ts: credential-based forward auth flow tests
(redirect, portal form, login, session cookie, forged cookie rejection)
- Add forward-auth-oauth.spec.ts: full OAuth forward auth flow tests
including user-based access (allowed/denied), group-based access,
access revocation, and credential login coexisting with OAuth
- Add waitForStatus helper for polling specific HTTP status codes
- Expand portal.spec.ts with OAuth button visibility, URI scheme
rejection, and strict alert selector tests
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>