ci(deploy): SKIP_DEV_TESTS flag and a dev rollback button

[saqibmanan]

Lets dev deploys run without the CivicDataSpace-test gates while the test owner is away, and adds a one-click rollback for dev.

Skip flag: repo variable SKIP_DEV_TESTS

• Off (default): variable unset. Nothing changes.
• On: gh variable set SKIP_DEV_TESTS --body true -R CivicDataLab/<repo>, or Settings → Secrets and variables → Actions → Variables.
• Back off: gh variable delete SKIP_DEV_TESTS -R CivicDataLab/<repo>.

When it's on, a dev deploy:

• skips Smoke and Functional tests;
• shows a green Tests skipped (SKIP_DEV_TESTS) job with a notice;
• still runs the post-deploy step (promote / Finalize Deploy), so the deploy is recorded as the rollback point.

main ignores the flag: prod deploys are always gated.

Rollback button

Actions → this workflow → Run workflow → branch dev → tick rollback.

This skips the build and runs the existing rollback job:

• Frontend: relinks the release from before the last deploy, then records it as last-known-good.
• Backend: restores the image that was live before the last deploy.

The run is green when the rollback succeeds. The rollback is ignored on main. As before, migrations are not reverted.

Checks

• actionlint is clean.
• On a dev push, the flag decides whether Smoke Tests or Tests skipped runs. Rollback only fires when tests fail, or from the button.