fix(workouts): hold training load through unscored days

A day without a stored training impulse was read as a rest day, so a
watch left off or a nightly run that had not happened yet pulled
fitness and fatigue toward zero. Such a day is now not rated: the
averages hold through it, the series marks it, and the card says how
many of the last 42 days were rated. A scored day of 0 stays rest. The
figures describe the last stored day rather than always yesterday.

src/app/api/workouts/__tests__/canonical-dedup.test.ts

@@ -461,6 +461,8 @@ describe("GET /api/workouts — training load (v1.44)", () => {
       asOf: yesterday,
       daysCovered: 50,
       trainingDays: 50,
+      recentRatedDays: 42,
+      recentDays: 42,
       warmingUp: false,
     });
     const later = await (await GET(makeRequest("?offset=100"))).json();