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

playwright.config.ts + tests/e2e/{apex,tenant,health}.spec.ts. make e2e for local. CI e2e job opt-in via RUN_E2E repo variable. OIDC click-through deferred to when stage is up.

Refs: M5.3

package.json

@@ -14,7 +14,9 @@
     "start": "next start --port 3000",
     "lint": "eslint . --max-warnings 0",
     "typecheck": "tsc --noEmit",
-    "test": "vitest run --coverage"
+    "test": "vitest run --coverage",
+    "e2e": "playwright test",
+    "e2e:install": "playwright install --with-deps chromium"
   },
   "dependencies": {
     "next": "16.2.6",
@@ -23,6 +25,7 @@
     "react-dom": "19.0.0"
   },
   "devDependencies": {
+    "@playwright/test": "^1.60.0",
     "@types/node": "20.16.10",
     "@types/react": "19.0.1",
     "@types/react-dom": "19.0.1",