Retire the guardian toggle over a pref nothing reads

The evidence disclosure stopped honouring showEvidenceByDefault in
v1.4.27 and the owner surface retired the control with it — but the
managed-record coach form still offered the switch, silently governing
nothing. Remove the control, the managed-schema pick, the response
field, and the label in all six locales; the strict schema now refuses
the key outright.

src/lib/record-settings/configuration.ts

@@ -124,7 +124,6 @@ const managedCoachPreferencesSchema = coachPrefsSchema
     tone: true,
     verbosity: true,
     excludeMetrics: true,
-    showEvidenceByDefault: true,
     defaultWindow: true,
     dataClusters: true,
   })