feat(workouts): accept an optional HR series on the batch contract

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.

docs/api/openapi.yaml

@@ -834,6 +834,35 @@ paths:
                                 - t
                         required:
                           - geometry
+                      samples:
+                        minItems: 1
+                        maxItems: 30000
+                        type: array
+                        items:
+                          type: object
+                          properties:
+                            t:
+                              type: string
+                              format: date-time
+                              pattern: ^(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))T(?:(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d(?:\.\d+)?)?(?:Z|([+-](?:[01]\d|2[0-3]):[0-5]\d)))$
+                            hr:
+                              type: integer
+                              minimum: 20
+                              maximum: 300
+                            speedMs:
+                              type: number
+                              minimum: 0
+                              maximum: 50
+                            power:
+                              type: number
+                              minimum: 0
+                              maximum: 3000
+                            cadence:
+                              type: number
+                              minimum: 0
+                              maximum: 400
+                          required:
+                            - t
                     required:
                       - sportType
                       - startedAt
@@ -4322,6 +4351,10 @@ components:
           anyOf:
             - $ref: "#/components/schemas/WorkoutRouteGeometry"
             - type: "null"
+        samples:
+          anyOf:
+            - $ref: "#/components/schemas/WorkoutHrSeries"
+            - type: "null"
         canonicalId:
           type: string
       required:
@@ -4342,6 +4375,7 @@ components:
         - externalId
         - metadata
         - route
+        - samples
         - canonicalId
       additionalProperties: false
     WorkoutRouteGeometry:
@@ -4358,6 +4392,18 @@ components:
         - geometry
         - sampleTimestamps
       additionalProperties: false
+    WorkoutHrSeries:
+      type: object
+      properties:
+        sampleCount:
+          type: integer
+          minimum: 0
+          maximum: 9007199254740991
+        samples: {}
+      required:
+        - sampleCount
+        - samples
+      additionalProperties: false
     BatchWorkoutsResponse:
       type: object
       properties: