fix(charts): name a folded point of steps as a daily average

A week or month point of a cumulative metric is the average daily total,
which keeps the axis comparable with the 7, 30 and 90 day tabs. The
caption said "Weekly avg", which reads as an average week's total. Steps,
energy, distance, flights and daylight now say "Daily avg per week" or
"per month" on the caption and in the tooltip, in all seven languages;
level metrics keep the plain average.

src/components/charts/health-chart.tsx

@@ -59,6 +59,7 @@ import type {
   ComparisonBaseline,
 } from "@/lib/dashboard-layout";
 import { CUMULATIVE_HK_TYPES } from "@/lib/measurements/apple-health-mapping";
+import { bucketCaptionKey } from "@/lib/charts/bucket-caption";
 import type { MeasurementType } from "@/generated/prisma/client";
 import { ChartOverlayControls } from "./chart-overlay-controls";
 import { ChartDataTable, type ChartDataTableColumn } from "./chart-data-table";
@@ -1018,8 +1019,9 @@ export function HealthChart({
             // v1.4.29.1 — cumulative HealthKit types (steps, active energy,
             // distance, flights, daylight) must reduce with sum, not the
             // per-sample average. The server already returns one row per
-            // day; a day that arrives as several rows (the coarser tiers
-            // of the "All" range) must still add up rather than average.
+            // day (or, for the coarser tiers of the "All" range, one row per
+            // week or month carrying its average day); a day that arrives
+            // as several rows must still add up rather than average.
             const isCumulative = CUMULATIVE_HK_TYPES.has(
               type as MeasurementType,
             );
@@ -1339,6 +1341,10 @@ export function HealthChart({
   // the decision separately" drift the visibleSlice doc-comment warns
   // about, and the two had already diverged on the windowing semantics.
   const activeBucket: ChartBucketType = visibleSlice?.bucketType ?? "day";
+  // What a folded point is: the average day of its week or month (a daily
+  // total's average for steps and the like). Named on the caption chip and
+  // in the tooltip.
+  const bucketCaption = bucketCaptionKey(activeBucket, types);
 
   const yDomain = useMemo<[number, number] | undefined>(() => {
     if (!chartDataWithCompare?.length) return undefined;
@@ -1730,13 +1736,12 @@ export function HealthChart({
             ) : (
               <h2 className="text-sm font-semibold">{title}</h2>
             )}
-            {activeBucket !== "day" && (
-              <span className="bg-muted/40 text-muted-foreground text-2xs hidden rounded-md px-1.5 py-0.5 font-medium tracking-wide uppercase sm:inline-flex">
-                {t(
-                  activeBucket === "week"
-                    ? "charts.bucketWeekly"
-                    : "charts.bucketMonthly",
-                )}
+            {bucketCaption && (
+              <span
+                data-slot="chart-bucket-caption"
+                className="bg-muted/40 text-muted-foreground text-2xs hidden rounded-md px-1.5 py-0.5 font-medium tracking-wide uppercase sm:inline-flex"
+              >
+                {t(bucketCaption)}
               </span>
             )}
             {/* v1.4.16 phase B8 — comparison caption. Inline with the
@@ -2260,7 +2265,11 @@ export function HealthChart({
                       return (
                         <RichChartTooltip
                           active
-                          label={dateLabel}
+                          label={
+                            bucketCaption
+                              ? `${dateLabel} · ${t(bucketCaption)}`
+                              : dateLabel
+                          }
                           rows={rows}
                         />
                       );