Boards can chart each app's p75 load and INP per day from an app_vital source #3201

Boards (src/boards/sources.ts) can chart the forge's own visitors (reach, page_vital) but not an app's.

Done looks like:

• [ ] A new app_vital source gives rows of (day, app, p75 load, p75 INP, reports) over the board's range, using nearest-rank as page_vital does.
• [ ] Only an admin or the app's owner sees an app's rows, as the app's settings page already decides.
• [ ] A test has two apps with known reports and checks each p75 per day, and checks that a stranger gets no rows.

Files: src/boards/sources.ts, a test.