chore(ci): drop the eight legacy workflows that authenticate with the dead DEPLOY_KEY

[rubenvdlinde]

Removes the eight legacy release/sync workflows that authenticate with the SSH DEPLOY_KEY.

Why

DEPLOY_KEY is dead. release-workflow.yaml and release-stable.yaml failed on 2026-08-08 at the Checkout Code step:

Temporarily overriding GIT_SSH_COMMAND="/usr/bin/ssh" -i "$RUNNER_TEMP/…"
git@github.com: Permission denied (publickey).   (×3 attempts)
##[error]fatal: Could not read from remote repository.

That is a second dead credential, independent of PROJECT_TOKEN — an SSH deploy key rather than a token, so rotating the token does not touch it.

Why delete rather than rotate

These are the previous workflow generation, and it has already been replaced. beta carries only the current .yml set — release-beta.yml, release-stable.yml, sync-to-beta.yml, branch-protection.yml — and contains none of these files. development is the same. main is the only branch still holding them, because a promotion adds files without removing the ones it superseded.

Last run of each, any branch:

workflow	last run
beta-release.yaml	2026-02
release-beta.yaml	never run
release-stable.yaml	failure, 2026-08-08
release-unstable.yaml	2026-02 / 03
release-workflow.yaml	failure, 2026-08-08
sync-beta.yaml · sync-dev.yaml · unstable-release.yaml	2026-03

Nothing here has succeeded since March. Issuing a new write-capable deploy key to keep them alive would mint a credential for workflows that are already superseded.

The same generation also fails on saadmk11/changelog-ci@v1.1.2, a third-party Docker action that no longer builds — more evidence that this set is stale rather than broken.

What this does and does not change

Does not change: nothing that currently succeeds. Every one of these is either failing or last-green five months ago.

Does change, and worth stating: after this merges, main has no release workflow at all until the next beta → main promotion brings release-stable.yml across. Today it has one that fails on checkout, so this is not a loss of working function — but it is a real gap, and the one-step remedy is that promotion. Flagging rather than bundling it, because a release-path change belongs in its own decision.

Out of scope, deliberately: pr-check.yaml, pull-request-from-branch-check.yaml, pull-request-lint-check.yaml, push-development-to-beta.yaml and branch-policy.yml are from the same stale generation but do not use DEPLOY_KEY, so they are not touched here.