fix(sleep): reconstruct an ordered WHOOP hypnogram timeline

WHOOP's v2 API returns only per-stage sleep duration totals — no onset
timestamps, no hypnogram endpoint. The mapper stamped all five stage
totals on the one sleep-END instant, so the hypnogram reconstructed
every stage as a span touching the night's right edge: bars stacked
right-aligned with no clock times whenever WHOOP was the sole source.

Lay the asleep stages back-to-back from sleep onset in a fixed
physiological order (AWAKE lead, then CORE → DEEP → REM), emitting one
timed row per segment with measuredAt at that segment's end and a
distinct indexed externalId. IN_BED stays a single envelope row over the
whole window. The existing reader and renderer are untouched — they now
see distinct per-segment instants and place each block at its own time.

The order is synthesised, not measured, so every reconstructed row is
flagged and the night DTO carries a per-session `reconstructed` boolean
(GET /api/sleep/night, regenerated OpenAPI). The client renders the
hypnogram but labels it an approximate layout and never recomputes;
real-series sources (Apple Health, Withings, Fitbit) stay false.

src/lib/openapi/routes/measurements.ts

@@ -200,6 +200,11 @@ const sleepSessionResource = z.object({
   inBedMinutes: z.number().int().nonnegative().nullable(),
   awakeMinutes: z.number().int().nonnegative().nullable(),
   awakenings: z.number().int().nonnegative(),
+  reconstructed: z
+    .boolean()
+    .describe(
+      "True when the source has no per-stage onset timestamps and the server synthesised a contiguous timeline in a fixed physiological order (WHOOP). The client renders the hypnogram but labels it an approximate layout and never recomputes. False for real-series sources (Apple Health / Withings / Fitbit).",
+    ),
   stages: z.record(sleepStageEnum, z.number().int().nonnegative()),
   segments: z.array(sleepSegmentResource),
 });