Home opens with a KPI row: landings per hour, live version, median check time #2739

Part of the former #2665.

Done:

• [ ] one small module computes plain data, and home renders it server-side as a row of KPIs: real landings per hour (non-empty commits on main, with a 24 h sparkline), the live version and when it went live, and the median check time over 24 h. Each KPI links to its board or page
• [ ] DESIGN.md tokens only, no layout shift, wraps readably at 360px
• [ ] test: seeded commits and checks give the expected numbers, and an empty commit is not counted

Parked by the crew: the check failed ("dev's vocabulary never reaches a studio page > every studio page — home, app, tell, working, look, shipped, search and the three lists: no dev word, the studio chrome, the security floor, and a page a diff would never fit in") and the decider saw no point in another try (pull #2863 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check failed ("design check: nothing added outside the system (#2678) > the tree is no worse than its baseline") and the decider saw no point in another try (pull #2865 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check failed ("dev's vocabulary never reaches a studio page > every studio page — home, app, tell, working, look, shipped, search and the three lists: no dev word, the studio chrome, the security floor, and a page a diff would never fit in") and the decider saw no point in another try (pull #2863 closed)
2. the check failed ("design check: nothing added outside the system (#2678) > the tree is no worse than its baseline") and the decider saw no point in another try (pull #2865 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Split into #2870 and #2871. Both pulls built the KPIs and failed guards on the page, not the numbers. #2863 put a dev word (commit/merge) on home, which is a studio page, and #2865 added styles outside the design system's baseline. #2870 is the data module alone, with its test. #2871 renders the row, names both guards, the studio words to use, and the tokens-only rule, and lists the three tests to run before pushing. #2740 and #2741 now wait on #2871.