forgepulse: the dashboard now shows when its numbers were last refreshed

forgepulse shows the age of its own data: the homepage now reads the most recent successful sync run — already recorded in the sync_runs table but never surfaced — and renders it next to the git-ref pill as Updated <UTC> · <local> (Xh Ym ago), ticking every minute (d4c5e85). Traffic history is only as useful as the moment it was collected, and until now the dashboard gave no way to tell a stale snapshot from a fresh one. The change touches two new frontend modules plus tests for the relative-time formatter and the API field behind it.