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

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

server/channels/api4/config.go

@@ -239,7 +239,9 @@ func updateConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 			c.Err = model.NewAppError("updateConfig", "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))
+		}
 		return
 	}
 
@@ -281,7 +283,9 @@ func getEnvironmentConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 	})
 
 	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
-	w.Write([]byte(model.StringInterfaceToJSON(envConfig)))
+	if _, err := w.Write([]byte(model.StringInterfaceToJSON(envConfig))); err != nil {
+		c.Logger.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func patchConfig(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -386,7 +390,9 @@ func patchConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 			c.Err = model.NewAppError("patchConfig", "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))
+		}
 		return
 	}