CI: lightweight checks on PRs (follow-up to #62) #87

#62 proposed push/PR checks (bootstrap, version/new/build, GUI smoke) on macOS, Windows and Ubuntu 22.04. The goal is right: today build breaks surface at tag time, or only if a release-test/** branch is pushed by hand. It was closed because of how it was shaped, not because of the idea. Notes for a future version:

Keep from #62

• A separate workflow with contents: read, no caches, persist-credentials: false, so fork PRs can't touch release builds or the tjs cache. Don't just add a PR trigger to release.yml.
• Stricter smoke validation than release.yml's || true + grep: check the exit code and timeouts, and reject a crash that happens after SMOKE RESULTS.

Do differently

• Triggers: pull_request + push to main only, with paths-ignore for docs/** and *.md. ci: check builds and GUI smoke tests on pull requests #62 ran every push on every branch, so same-repo PR branches ran twice and docs commits paid a full uncached Linux tjs build (15–25 min).
• Read TJS_VERSION from setup.sh instead of setting it a fourth time.
• Share the GLIBC/GLIBCXX ceiling and macOS launcher checks with release.yml (one script both call), not a second copy that drifts.
• Smoke validation: don't hard-code the result keys; adding a check to test/smoke.html shouldn't require a CI edit.
• Keep the harness small and close to the repo's existing style (shell/JS). Avoid a large standalone Python harness.

Gaps worth deciding on

• Packaging isn't covered. Recent release fixes (e.g. c2a3b5e, the Windows zip missing install.ps1) were packaging, not build.
• No arm64 Linux/Windows legs.
• The test/*/ checks (gates, wire-lines, update-*) don't run anywhere automatically. A headless subset may be worth more than another build.

Until then: push a release-test/<name> branch before tagging for a full dry run.