fix(analytics): all-time extremes and range deltas count one source per day

The all-time weight, blood-pressure and pulse figures the insight features
carry averaged every raw row, so a device that samples densely outweighed the
readings the source ladder prefers on the same days. They now keep one source
per day, like the dashboard's all-time figures.

The period-over-period range delta averaged readings. For step-like totals
the current window still holds the last day and a half as many small
samples, so the average collapsed; it now compares average daily totals. For
sleep it averaged stage segments and in-bed envelopes; it now compares
average nights of time asleep. The API descriptions say which.

src/lib/analytics/__tests__/range-delta-per-period.test.ts

@@ -0,0 +1,93 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  readRollupBuckets: vi.fn(),
+  findMany: vi.fn(),
+}));
+
+vi.mock("@/lib/db", () => ({
+  prisma: { measurement: { findMany: mocks.findMany } },
+}));
+vi.mock("@/lib/rollups/measurement-rollups", () => ({
+  readRollupBuckets: mocks.readRollupBuckets,
+}));
+vi.mock("@/lib/rollups/measurement-read", () => ({
+  loadUserSourcePriority: vi.fn(async () => null),
+}));
+vi.mock("@/lib/rollups/measurement-read-wmy", () => ({
+  aggregateWmyBuckets: vi.fn(),
+  readBestGranularityRollups: vi.fn(async () => null),
+}));
+vi.mock("@/lib/tz/resolver", () => ({
+  resolveUserTimezone: vi.fn(async () => "UTC"),
+}));
+
+import { computeRangeDelta } from "@/lib/analytics/range-delta";
+
+const DAY_MS = 86_400_000;
+const NOW = Date.UTC(2026, 5, 30, 12);
+
+function dayRow(daysAgo: number, total: number, samples: number) {
+  const bucketStart = new Date(Date.UTC(2026, 5, 30) - daysAgo * DAY_MS);
+  return {
+    bucketStart,
+    count: samples,
+    mean: total / samples,
+    minValue: 0,
+    maxValue: total,
+    sd: null,
+    slope: null,
+    r2: null,
+    computedAt: bucketStart,
+  };
+}
+
+beforeEach(() => {
+  mocks.readRollupBuckets.mockReset();
+  mocks.findMany.mockReset();
+});
+
+describe("computeRangeDelta — per-day and per-night metrics", () => {
+  it("compares average daily step totals, not the mean of the readings", async () => {
+    // Six complete days of 8,000 in the previous week, and in the current
+    // week five drained days plus today still arriving as 200 samples.
+    mocks.readRollupBuckets.mockResolvedValue([
+      ...[8, 9, 10, 11, 12, 13].map((d) => dayRow(d, 8000, 1)),
+      ...[1, 2, 3, 4, 5].map((d) => dayRow(d, 8000, 1)),
+      dayRow(0, 4000, 200),
+    ]);
+
+    const result = await computeRangeDelta("u", "ACTIVITY_STEPS", "7d", NOW);
+
+    expect(result.granularity).toBe("DAY");
+    expect(result.previous).toMatchObject({ count: 6, mean: 8000 });
+    expect(result.current.count).toBe(6);
+    expect(result.current.mean).toBeCloseTo((5 * 8000 + 4000) / 6, 6);
+    expect(result.current.sum).toBeCloseTo(44_000, 6);
+  });
+
+  it("compares average nights of sleep, not the mean of stage rows", async () => {
+    const row = (iso: string, minutes: number, sleepStage: string) => ({
+      value: minutes,
+      measuredAt: new Date(iso),
+      sleepStage,
+      source: "APPLE_HEALTH",
+      deviceType: null,
+    });
+    // Two nights: 7 h asleep (split into three stage rows plus an in-bed
+    // envelope) and 6 h asleep.
+    mocks.findMany.mockResolvedValue([
+      row("2026-06-28T01:00:00.000Z", 480, "IN_BED"),
+      row("2026-06-28T02:00:00.000Z", 180, "CORE"),
+      row("2026-06-28T04:00:00.000Z", 120, "DEEP"),
+      row("2026-06-28T06:00:00.000Z", 120, "REM"),
+      row("2026-06-29T06:00:00.000Z", 360, "ASLEEP"),
+    ]);
+
+    const result = await computeRangeDelta("u", "SLEEP_DURATION", "7d", NOW);
+
+    expect(result.granularity).toBe("live");
+    expect(result.current.count).toBe(2);
+    expect(result.current.mean).toBeCloseTo(390, 6);
+  });
+});