Sync GH: push commits+tags, close stale issues, migrate open GitLab issues to GitHub (with new GH ids tracked alongside GL ids in trajectory DB)

Full content on GitLab: https://gitlab.com/trustmybot/plugin/-/issues/2935

(Tri-source sync schema landed in MR !208 but mirror logic not yet bidirectional; this issue is a stub for v0.7.x board review.)