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.

docs/api/openapi.yaml

@@ -8982,6 +8982,11 @@ components:
                   type: integer
                   minimum: 0
                   maximum: 9007199254740991
+                reconstructed:
+                  type: boolean
+                  description: 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:
                   type: object
                   propertyNames:
@@ -9047,6 +9052,7 @@ components:
                 - inBedMinutes
                 - awakeMinutes
                 - awakenings
+                - reconstructed
                 - stages
                 - segments
               additionalProperties: false
@@ -9102,6 +9108,11 @@ components:
                 type: integer
                 minimum: 0
                 maximum: 9007199254740991
+              reconstructed:
+                type: boolean
+                description: 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:
                 type: object
                 propertyNames:
@@ -9167,6 +9178,7 @@ components:
               - inBedMinutes
               - awakeMinutes
               - awakenings
+              - reconstructed
               - stages
               - segments
             additionalProperties: false