feat(timeline): serve lab markers as value lines

The timeline showed a lab report as an event on the axis, but the lines
under the lanes could only be measurements. A lab marker can now be named
in `values` as `lab:<biomarkerId>`, beside the measurement types and
`MOOD`, so one choice, one request and one stored list carry every line.

`GET /api/timeline` answers with `labSeries`, one entry per named marker
with its readings in the window as single points (lab values come a few a
year, so they are never averaged into buckets), each dated by the record's
local day, judged against its own window and linked to the report it was
read from when the caller may see documents. `availableLabs` lists every
marker the record has a numeric reading for, so a client offers only
those.

A reading stored in another unit than its marker's is converted through
the unit-conversion registry where the pair is known, and otherwise left
out and counted in `excluded`, never drawn on a scale it is not in. A
marker id that is not in the record yields no line instead of a 422, so a
stored choice survives a deleted marker; ids are capped at 24 a request.

Refs #1299

src/app/api/timeline/route.ts

@@ -69,6 +69,7 @@ export const GET = apiHandler(async (request: Request) => {
       lanes: timeline.lanes.length,
       items: timeline.lanes.reduce((n, l) => n + l.items.length, 0),
       series: timeline.series.length,
+      labSeries: timeline.labSeries.length,
       notable: timeline.notable.length,
     },
   });