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/components/workouts/__tests__/training-load-card.test.tsx

@@ -17,6 +17,8 @@ const OK: TrainingLoad = {
   tsb: -7.6,
   daysCovered: 30,
   trainingDays: 18,
+  recentRatedDays: 30,
+  recentDays: 30,
   warmingUp: true,
   series: [],
 };
@@ -36,6 +38,13 @@ describe("<TrainingLoadCard>", () => {
     expect(html).toMatch(/training-load-fatigue[^]*?>62</);
     expect(html).toContain("-8");
     expect(html).toContain("Based on 30 days so far");
+    expect(html).not.toContain('data-slot="training-load-coverage"');
+  });
+
+  it("says how many recent days were rated when some were not", () => {
+    const html = render({ ...OK, recentRatedDays: 25, recentDays: 42 });
+    expect(html).toContain('data-slot="training-load-coverage"');
+    expect(html).toContain("25 of the last 42 days have heart-rate data");
   });
 
   it("signs a positive form and drops the warm-up note once covered", () => {

src/components/workouts/training-load-card.tsx

@@ -47,6 +47,17 @@ export function TrainingLoadCard({
           ))}
         </dl>
         <p className="text-sm">{t("insights.workouts.load.explainer")}</p>
+        {trainingLoad.recentRatedDays < trainingLoad.recentDays ? (
+          <p
+            className="text-muted-foreground text-xs"
+            data-slot="training-load-coverage"
+          >
+            {t("insights.workouts.load.coverage", {
+              rated: trainingLoad.recentRatedDays,
+              days: trainingLoad.recentDays,
+            })}
+          </p>
+        ) : null}
         {trainingLoad.warmingUp ? (
           <p className="text-muted-foreground text-xs">
             {t("insights.workouts.load.warmingUp", {