Get the first-ping waiting/received card data for a check

The REST equivalent of the dashboard's "listening for your first heartbeat" card. received becomes true once the monitor has reported in any way — including an outstanding /start that was later cancelled or consumed by detection — using the same predicate the dashboard's own card polls against (the monitor's state alone cannot tell a cancelled start from a monitor that was truly never pinged, so this endpoint also looks at its pings, same as the dashboard).

signal_word/instruction/command are a pure function of the monitor's own configuration (monitor_type, ci_provider), never of whether it has reported yet — they stay populated after received becomes true, unlike the HTML fragment which stops rendering them. command is omitted for http monitors, which probe automatically and so have no copy-paste command.

test_ping_only separates "we have heard from the console's own test ping" from "your job has reported". Without it, pressing POST /api/v1/checks/{id}/test-ping on a monitor nothing has reported to flips received to true and a client that reads only received tells the user their integration works.

404 if the check does not exist in the authenticated project (no existence oracle).

Console stability note. This response is shaped by a console screen: the fields are the ones that screen draws, in the grouping it draws them in. It stays published because reading it is a reasonable thing to automate, and no field will be removed or change meaning without a version. Fields may be ADDED as the screen grows, so treat unknown keys as normal rather than as an error.