feat(test): M5.3 — Playwright e2e harness for the dev stack

Adds the M5.3 deliverable scoped to local-dev (stage doesn't exist yet,
so the CI e2e job is gated behind the repo variable RUN_E2E='true' —
defaults off).

Layout:
  playwright.config.ts   chromium project; baseURL defaults to
                         http://acme.localhost:3000 (subdomain routing
                         fires). PLAYWRIGHT_BASE_URL / APEX_URL / etc.
                         env vars override for stage.
  tests/e2e/apex.spec.ts        landing page renders
  tests/e2e/tenant.spec.ts      signed-out dashboard shows Sign in
                                button; unknown slug returns 404
  tests/e2e/health.spec.ts      every dev-stack endpoint reachable
                                (portal /api/auth/providers, tenant-
                                registry /healthz, KC realm metadata)

Run locally with the full dev stack up:

  cd platform/orca-platform && make dev-up
  cd platform/tenant-registry && make dev
  cd platform/portal && make dev
  cd platform/portal && make e2e

OIDC click-through not asserted yet — Keycloak in headless mode is
flaky and depends on a stable test-user password. The current gate
(Sign-in button visible) catches the more common 'auth completely
broken' regression; the deeper smoke lands when stage has its own
test fixture.

tsconfig now excludes tests/e2e so vitest + tsc don't fight over
Playwright type imports.

Refs: M5.3

Makefile

@@ -4,13 +4,15 @@
 
 help:
 	@echo "portal targets:"
-	@echo "  make install      pnpm install"
-	@echo "  make dev          pnpm dev (http://localhost:3000)"
-	@echo "  make test         pnpm test (vitest + coverage)"
-	@echo "  make lint         pnpm lint"
-	@echo "  make typecheck    pnpm typecheck"
-	@echo "  make build        pnpm build (Next.js production build)"
-	@echo "  make docker       build local image (portal:dev)"
+	@echo "  make install       pnpm install"
+	@echo "  make dev           pnpm dev (http://localhost:3000)"
+	@echo "  make test          pnpm test (vitest + coverage)"
+	@echo "  make lint          pnpm lint"
+	@echo "  make typecheck     pnpm typecheck"
+	@echo "  make build         pnpm build (Next.js production build)"
+	@echo "  make e2e           pnpm e2e (Playwright; needs dev stack + tenant-registry + portal running)"
+	@echo "  make e2e-install   one-time browser install"
+	@echo "  make docker        build local image (portal:dev)"
 
 install:
 	@pnpm install --frozen-lockfile
@@ -30,6 +32,12 @@ typecheck:
 build:
 	@pnpm build
 
+e2e:
+	@pnpm e2e
+
+e2e-install:
+	@pnpm e2e:install
+
 docker:
 	@docker build -t portal:dev .