perf(ci): optimize GitHub Actions — Playwright cache, timeout, Docker cache, codecov #3791

Context

Vue CI runs take 28-35 min (2 parallel jobs). Heavy dev sessions burn through GitHub Actions minutes fast. The comes-io org hit its free tier limit.

Fixes needed

1. Cache Playwright browsers

Playwright downloads browsers on every run (~5 min). Cache them:

- uses: actions/cache@v4
  with:
    path: ~/.cache/ms-playwright
    key: playwright-${{ hashFiles('package-lock.json') }}

Saves ~15 min per E2E run.

2. Set job timeouts

No timeout set. Add:

jobs:
  lint-unit-build:
    timeout-minutes: 15
  e2e:
    timeout-minutes: 30

3. Docker layer cache in build.yml

Add GHA cache to build-push-action. Saves ~3-5 min per build.

4. Skip CI on merge push

CI runs on both PR and push to master — double run on every merge.

5. Fix codecov slug

All downstream repos report to pierreb-devkit/Vue instead of their own repo:

slug: ${{ github.repository }}

6. Standardize Node version

Release workflow uses v18, CI uses lts/*. Standardize to lts/*.

Impact

These optimizations propagate to all downstream projects via stack updates.