fix(fitbit): show the retired card only to an account that had Fitbit

After the Web API turndown every account still saw a Fitbit card that
can no longer connect. The status entry now publishes
retirement.offered: false once the API is gone for an account with no
Fitbit connection, no Fitbit app of its own and no Fitbit data, and the
connections panel leaves the card out. Accounts that had Fitbit keep it
with the retirement notice.

docs/api/openapi.yaml

@@ -79488,10 +79488,16 @@ components:
                 - google-health
               description: The integration that reads the same Fitbit and Pixel devices. Moving needs a fresh consent; the Fitbit
                 grant cannot be carried over.
+            offered:
+              type: boolean
+              description: "Whether the Fitbit card is shown. False once `ended` for an account that never connected Fitbit, has no
+                Fitbit app of its own and holds no Fitbit data: there is nothing to explain the move for. True before
+                the turndown and for every account that had Fitbit."
           required:
             - endsOn
             - ended
             - successor
+            - offered
           additionalProperties: false
         health:
           anyOf: