build(ci): key Playwright browser cache on .service-versions

[iloveitaly]

Motivation

The Playwright browser cache was keyed on hashFiles('uv.lock', '.service-versions'), which invalidates on any lockfile or service-version change. A more precise key is the Playwright package version itself, which is what determines the downloaded Chromium revision.

This replaces lockfile scraping / awk with the same jq -r pattern already used for postgres in just/database.just.

Description

• Persist playwright in .service-versions via write-versions (from importlib.metadata).
• In CI, read that field with jq -r '.playwright' and use it as the actions/cache key.
• Guard the new field with a functional version-alignment test.

Screenshots / Test

Local verification: jq -r '.playwright' .service-versions returns 1.62.0, matching the installed Playwright package. The resulting cache key is Linux-playwright-1.62.0.

Links

• Related: build(ci): use direct apt-get install and cache playwright browsers #104 (Playwright browser cache)