feat(workouts): show fitness, fatigue and form from the stored training impulse

The first page of the workout list now carries the fitness-fatigue model
over the day-total heart-rate impulse the nightly strain run already
stores: fitness as the 42-day and fatigue as the 7-day exponentially
weighted average, form as their difference. A day without a stored impulse
counts as rest. It needs 28 days and three training days, flags the first
six weeks as warming up, and reads in the person's own units only. The
workouts page shows the three figures above the list.

docs/api/openapi.yaml

@@ -48526,6 +48526,10 @@ components:
             - offset
             - droppedDuplicates
           additionalProperties: false
+        trainingLoad:
+          description: v1.44 — on the first page (`offset=0`) only, account-wide whatever the filter. Absent on later pages and
+            older servers.
+          $ref: "#/components/schemas/WorkoutTrainingLoad"
       required:
         - workouts
         - meta
@@ -48602,6 +48606,94 @@ components:
         - hasRoute
         - hasHrSeries
       additionalProperties: false
+    WorkoutTrainingLoad:
+      anyOf:
+        - type: object
+          properties:
+            status:
+              type: string
+              const: ok
+            asOf:
+              type: string
+              description: The last scored UTC day the figures describe.
+            ctl:
+              type: number
+              description: "Fitness: 42-day exponentially weighted TRIMP."
+            atl:
+              type: number
+              description: "Fatigue: 7-day exponentially weighted TRIMP."
+            tsb:
+              type: number
+              description: "Form: fitness minus fatigue at `asOf`."
+            daysCovered:
+              type: integer
+              minimum: -9007199254740991
+              maximum: 9007199254740991
+            trainingDays:
+              type: integer
+              minimum: -9007199254740991
+              maximum: 9007199254740991
+            warmingUp:
+              type: boolean
+              description: "True below 42 covered days: both averages start at zero."
+            series:
+              type: array
+              items:
+                type: object
+                properties:
+                  day:
+                    type: string
+                  ctl:
+                    type: number
+                  atl:
+                    type: number
+                  tsb:
+                    type: number
+                required:
+                  - day
+                  - ctl
+                  - atl
+                  - tsb
+                additionalProperties: false
+              description: The trailing 90 days, oldest first; `tsb` is form going into the day.
+          required:
+            - status
+            - asOf
+            - ctl
+            - atl
+            - tsb
+            - daysCovered
+            - trainingDays
+            - warmingUp
+            - series
+          additionalProperties: false
+        - type: object
+          properties:
+            status:
+              type: string
+              const: insufficient
+            reason:
+              type: string
+              enum:
+                - no_impulse_history
+                - too_little_history
+            daysCovered:
+              type: integer
+              minimum: -9007199254740991
+              maximum: 9007199254740991
+            trainingDays:
+              type: integer
+              minimum: -9007199254740991
+              maximum: 9007199254740991
+          required:
+            - status
+            - reason
+            - daysCovered
+            - trainingDays
+          additionalProperties: false
+      description: "v1.44 — the fitness-fatigue model over the stored daily heart-rate training impulse (Banister TRIMP; a day
+        without a stored impulse counts as rest). Needs 28 days and three training days. TRIMP units: comparable with
+        the person's own past only."
     GetWorkoutResponse:
       type: object
       properties: