[ ] src/boards/sources.ts gains a source with: visitors per day, accounts active today / 7 days, total accounts, p75 LCP and INP per route, server p50/p95 per route
[ ] the owner sees it; a stranger does not
[ ] tests: seeded rows give the expected p75 and counts; a stranger's /boards/data for it is refused
Third part of #2674.
Done: