Deduplicate npm installs in Playwright workflow

[gkorland]

Parent issue

Part of #550 (CI Pipeline Optimization Analysis)

Problem

The Playwright workflow runs npm ci twice:

1. For frontend dependencies (working-directory: ./app)
2. For root dependencies / Playwright (npm ci at root level in the "Install Playwright" step)

Solution

Consolidate or restructure the npm installs. Options:

• Install root + frontend deps in a single step
• Move Playwright to the frontend package if appropriate
• At minimum, ensure both are cached via setup-node with cache: 'npm'

Estimated savings

~5s per shard

Effort

Low