fix(settings): let the display name change after the setup flow

The setup flow asks for the name the greeting and the reports use, and
the profile route has always accepted it, but no settings surface offered
the field and /api/auth/me did not publish it. A name chosen on the
first day stayed for good.

The account payload now carries `displayName`, the profile card shows the
field beside the username and saves it with the rest of the profile, and
an emptied field clears the name.

src/app/api/auth/me/route.ts

@@ -391,6 +391,10 @@ export const GET = apiHandler(async () => {
     // resolved `ai.capabilities.coach` and `modules.coach` below, which fold
     // in the record's own opt-out, the operator's switches and the grant.
     disableCoach: user.disableCoach ?? false,
+    // The name the app addresses the account by (dashboard greeting,
+    // reports). Set in the setup flow and edited on the profile card, which
+    // seeds its field from here.
+    displayName: user.displayName ?? null,
     // v1.7.0 — health-record export identity fields. All optional.
     fullName: user.fullName ?? null,
     insurerName: user.insurerName ?? null,