Drives the full world/travel flow in Chromium via Playwright against the
live API and seeded Postgres, capturing the three required desktop
viewports and comparing them against the accepted design reference.
Fixes two evidenced defects found during verification:
- world-page scene sizing overflowed the viewport at all three required
desktop sizes, pushing the footer (and, at 1440x900/1366x768, the travel
button) below the fold; scene height now accounts for surrounding chrome
so nothing is clipped.
- the generic HTTP-failure fallback message was hardcoded in English while
the rest of the UI is German; now uses a matching German string.
Adds Playwright as a web devDependency for this and future browser
verification passes (no product-code dependency).
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