feat(dashboard): send the glucose card in the owner's glucose unit

/api/dashboard/summary sent the glucose card's value in mg/dL with
unit null and a unitKey that reads mg/dL, so a reader on mmol/L saw
the mg/dL number. The card now carries latestValue, secondaryValue
and sparkline in the record owner's glucose unit and names it in
unit, the field that wins over unitKey, as the sleep card already
does. Applied after the summary cache read, so a unit change shows
on the next request.

docs/api/openapi.yaml

@@ -71078,8 +71078,10 @@ components:
           anyOf:
             - type: string
             - type: "null"
-          description: Explicit unit token, set only on the `sleep` card (`h`, because its value is a per-night total in hours
-            rather than the canonical SLEEP_DURATION minutes). Null on every other kind.
+          description: "Explicit unit token. When set it wins over `unitKey`. Set on the `sleep` card (`h`, because its value is a
+            per-night total in hours rather than the canonical SLEEP_DURATION minutes) and, since v1.40.0, on the
+            `glucose` card: the record owner's glucose unit (`mg/dL` or `mmol/L`), with `latestValue`, `secondaryValue`
+            and `sparkline` converted to it (mmol/L to one decimal). Null on every other kind."
         sleepStages:
           anyOf:
             - type: object