Add E2E test workflow with Playwright in CI

[Wilfred007]

What

e2e.yml workflow exists and Playwright is configured but needs proper CI integration with backend + frontend services.

Why

E2E tests catch integration issues between frontend and backend that unit tests miss. Currently not enforced.

Scope

In scope: CI starts backend + frontend, runs Playwright, uploads report as artifact
Out of scope: Visual regression, cross-browser matrix

Acceptance Criteria

• E2E tests run on every PR touching frontend
• Backend and frontend started in CI
• Test report uploaded as artifact
• Failed tests block merge

Technical Context

• .github/workflows/e2e.yml — existing workflow
• frontend/playwright.config.ts — Playwright config
• frontend/e2e/ — 5 test files