PayGlue-OS v0.12.3: dependency updates

PayGlue-OS, the open-source version of PayGlue, is at v0.12.3. It brings the same dependency updates payglue.io got today: Celery 5.7 for the background jobs, Pinia 4 in the dashboard, and patch releases of Vite, Vue and Tailwind.

The release also draws the Creem logo from Creem's own mark, links the new trailer in the README, and asks contributors from outside the team to sign a contributor license agreement before their first pull request is merged.