Unify sleep-night reconstruction onto the canonical engine

Replace the divergent UTC-day night reconstructor in the Sleep Score with a
thin adapter over reconstructSleepNights, the shared engine the dashboard,
hypnogram, and doctor surfaces already read. The old path bucketed rows by UTC
calendar day and never deduplicated writers, so a multi-source night (WHOOP +
Apple Health for the same sleep) summed both writers and roughly doubled the
total. The adapter inherits session-clustering, local-wake-day keying, and
multi-source writer dedup, then derives the score-only fields the canonical
night does not carry: REM and Deep minutes from the stage map, the stage-
breakdown flag from any granular stage, and the midpoint from the asleep span.

Select source and deviceType in the Sleep Score read so the writer-dedup
ladder fires, and thread the user source priority through so the chosen writer
matches every other sleep surface. Round emitted asleep and in-bed minutes to
whole numbers, and round the per-stage map in the sleep-night DTO, matching the
integer contract the native client decodes.

A multi-source user's sleep score and the readiness score that folds it drop
once the double-count is removed, reflecting the true single-writer night.

docs/api/openapi.yaml

@@ -8661,7 +8661,9 @@ components:
                       - CORE
                       - DEEP
                   additionalProperties:
-                    type: number
+                    type: integer
+                    minimum: 0
+                    maximum: 9007199254740991
                   required:
                     - IN_BED
                     - AWAKE
@@ -8776,7 +8778,9 @@ components:
                     - CORE
                     - DEEP
                 additionalProperties:
-                  type: number
+                  type: integer
+                  minimum: 0
+                  maximum: 9007199254740991
                 required:
                   - IN_BED
                   - AWAKE