fix(workouts): read a day with activity data and no workout as rest

The strain run writes no impulse row on a day without a scorable workout
or active energy, so a rest day for someone without daily active energy
was never rated: fitness and fatigue held for months instead of
decaying, and the figures named the last stored day while the coverage
count ended there too.

A day without a stored impulse is now classified from the underlying
data: a workout on the day leaves it unrated, steps, heart rate or
active energy without a workout make it rest, and no data at all leaves
it unrated. The series runs to the day the strain run scores, so a
stretch without data after the last rated day shows in the coverage
count, and the card names the last rated day when it lies further back
than the day before.

docs/api/openapi.yaml

@@ -49472,8 +49472,8 @@ components:
               const: ok
             asOf:
               type: string
-              description: "The last UTC day with a stored impulse, at most yesterday: a nightly run that has not happened yet never
-                reads as a rest day."
+              description: The last rated UTC day, at most yesterday; the figures are those of this day. The series runs on to
+                yesterday, so a later stretch without data shows as unrated days.
             ctl:
               type: number
               description: "Fitness: 42-day exponentially weighted TRIMP."
@@ -49495,7 +49495,8 @@ components:
               type: integer
               minimum: -9007199254740991
               maximum: 9007199254740991
-              description: Days of the trailing `recentDays` (42, or fewer when covered less) with a stored impulse.
+              description: "Rated days of the trailing `recentDays` (42 up to yesterday, or fewer when covered less): a stored
+                impulse, or activity data without a workout."
             recentDays:
               type: integer
               minimum: -9007199254740991
@@ -49518,8 +49519,9 @@ components:
                     type: number
                   rated:
                     type: boolean
-                    description: "False for a day without a stored impulse (never scored): the averages held through it rather than counting
-                      it as rest."
+                    description: "False for a day that could not be rated: no stored impulse and no activity data (steps, heart rate, active
+                      energy), or a workout that was never scored. The averages held through it rather than counting it
+                      as rest. A day with activity data and no workout is rest (impulse 0)."
                 required:
                   - day
                   - ctl
@@ -49565,9 +49567,10 @@ components:
             - daysCovered
             - trainingDays
           additionalProperties: false
-      description: "v1.44 — the fitness-fatigue model over the stored daily heart-rate training impulse (Banister TRIMP; a
-        scored day without training is 0, a day without a stored impulse is not rated and the averages hold through it).
-        Needs 28 days and three training days. TRIMP units: comparable with the person's own past only."
+      description: "v1.44 — the fitness-fatigue model over the stored daily heart-rate training impulse (Banister TRIMP; a day
+        with activity data but no training is 0, a day with no data or an unscored workout is not rated and the averages
+        hold through it). Needs 28 days and three training days. TRIMP units: comparable with the person's own past
+        only."
     GetWorkoutResponse:
       type: object
       properties: