[MM-29049] Fix remaining errcheck errors in app, api4 and web package (#31307)

Co-authored-by: Claude <noreply@anthropic.com>

server/channels/api4/cluster.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 
 	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
 )
 
 func (api *API) InitCluster() {
@@ -31,5 +32,7 @@ func getClusterStatus(c *Context, w http.ResponseWriter, r *http.Request) {
 		c.Err = model.NewAppError("getClusterStatus", "api.marshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
 		return
 	}
-	w.Write(js)
+	if _, err := w.Write(js); err != nil {
+		c.Logger.Warn("Error while writing response", mlog.Err(err))
+	}
 }