E2E: Parallel test execution with multiple workers for faster CI

[phyllis-sy-wu]

Problem/Feature

E2E tests currently run with workers: 1 (sequential). The full suite takes ~15-20 minutes on CI. Most tests are independent and don't share state, so they can run concurrently.

Proposed Solution

• Set workers: 5 and fullyParallel: true in playwright.config.ts
• Per-worker port isolation: GraphiQL port = 3457 + workerIndex * 10, theme extension port = base + 2 (avoids EADDRINUSE)
• Global auth via globalSetup: authenticate once before workers start, save browser storageState to JSON, workers load it to skip redundant OAuth flows
• Workers copy CLI auth session files (XDG dirs) from global setup instead of each running auth login

Expected result: Suite time drops 50%

Prerequisites

Issue - #7269