Send adminUsername in /settings again

iOS app builds before Companion 2c9cc1c cannot decode /settings without
it, and App Review still tests such builds. A test keeps it in place.

api.go

@@ -1001,6 +1001,9 @@ func (a *App) getSettings(w http.ResponseWriter, r *http.Request) {
 		"geo":         a.geoStatus(),
 		"fingerprint": a.tls.Fingerprint(),
 		"logPath":     a.logPath,
+		// Required by iOS app builds before 2c9cc1c, which App Review
+		// still tests.
+		"adminUsername": a.username(cfg, who(r).UserID),
 	})
 }
 

main_test.go

@@ -350,6 +350,10 @@ func TestAPI(t *testing.T) {
 	bearer("POST", "/tokens", 403, map[string]string{"name": "more", "scope": "rw"})
 	bearer("DELETE", "/tokens/"+tok["id"].(string), 403)
 	bearer("GET", "/backup", 403)
+	// Older iOS app builds cannot decode /settings without it.
+	if call("GET", "/settings", nil, 200)["adminUsername"] != "admin" {
+		t.Fatal("/settings lacks adminUsername")
+	}
 
 	call("DELETE", "/peers/"+id, nil, 200)
 	if len(store.Get().Peers) != 0 {