forgepulse: rank-trend arrows in the repository signal table

forgepulse’s Repository signal table now carries a Billboard-chart-style up / down / stable indicator on every row, in both ranking modes, showing whether a repository moved since yesterday (9306fec). It tracks rank rather than the raw figure on purpose: clone volume ranks by total_clones, a cumulative counter that only ever grows, so diffing the value would read “up” almost every day regardless of real trend, while rank stays relative and keeps meaning.

The backend re-derives yesterday’s clone and human-attention rankings from the tables that are already day-keyed and retained — no new table — and diffs them against today’s through a shared dense-rank helper, so both modes break ties identically and a repository that did not exist yesterday falls back to “unknown” instead of inventing a direction.