ENG-217: Add Playwright E2E testing skill

[nihal467]

Summary

Adds a Copilot Playwright skill at playwright/SKILL.md — a single reference for writing E2E tests in CARE.

Contents

• When to use E2E vs unit/component tests
• Setup, run, debug, and report commands
• File organization (mirror routes, camelCase)
• 18 critical rules (deterministic fixture IDs, authenticated storageState, no .skip(), no random selection from lists, faker for created data, etc.)
• Form-testing checklist
• Patterns: Radix portal combobox, cascading combobox guard, Promise.all listener-before-action ordering, API setup via beforeEach with fail-fast, multi-role tests with try/finally context cleanup, file uploads with real fixtures, delete with double-confirm

Companion PR

Originally proposed in care_fe via ohcnetwork/care_fe#16480. Relocating to this central skills repo.

Closes

ENG-217