Extend POST /api/workouts/batch with an optional per-workout `samples`
array — a route-independent heart-rate series so indoor workouts still
yield a strain-relevant signal. Each entry is `{ t, hr?, speedMs?,
power?, cadence? }`; the array is capped at 30 000 points
(MAX_WORKOUT_HR_SAMPLES), covering a long endurance session sampled at
1 Hz while bounding the largest new workout-side write stream the same
way the 20 000-point route cap bounds the geometry.
Persistence rides the existing route-attachment path: the freshly
written workout id is resolved once (by composite key, or the manual
tuple), then both the route geometry and the HR series attach by FK
with skipDuplicates so a re-submitted batch stays idempotent. A workout
may carry both a GPS route and a canonical HR series, or just one.
GET /api/workouts/{id} returns the series alongside the route. OpenAPI
regenerated.
`samples` keeps first-write-wins/overwrite parity with the workout row
it hangs off: the 1:1 FK plus skipDuplicates means a re-ingest of an
existing workout never duplicates or mutates its series.