[M8-T02] Write editor E2E tests

## Task: M8-T02

**Milestone:** M8 - Playwright Tests (1 day)
**Feature:** RuleZ UI

## Description

Write E2E tests for the YAML editor functionality.

## Acceptance Criteria

- [ ] Test editor loads with content
- [ ] Test validation error display
- [ ] Test autocomplete functionality
- [ ] Test save keyboard shortcut

## Dependencies

- Depends on: M8-T01, M2-T01, M3-T02