[ankurmans]

Brings the workflow in line with the target flow in the CI handover.

• Draft pull requests and Dependabot's run nothing. The gate starts when a draft is marked ready (ready_for_review added to the trigger types). Fork pull requests are still skipped.
• check (the gate): a ready pull request runs lint, the affected tests and the build only if the change can reach it. A push to main, nightly and manual runs run lint and the build.
• full-suite: new job, every test, on push to main, nightly and manual runs only. Nothing waits for it, so it never holds back the build; a red suite turns the run red and GitHub mails the owner. It writes and caches the test map as before.
• timeout-minutes stays 360 on both jobs, runs-on is unchanged, nothing deploys.

Not done: there is no typecheck step because the repo is plain JavaScript (jsconfig.json only, no tsc script). No alert beyond GitHub's failed-run mail; the repo has no alert channel to post to.

This PR changes .github/, so its own run is the full suite and the build.