fix(pro-dummy): guard sockPort parseInt with || 3035 fallback

`parseInt(undefined, 10)` returns NaN, which would be silently passed
to ReactRefreshWebpackPlugin if devServer.port was ever absent. Falling
back to Shakapacker's default port (3035) surfaces a misconfiguration
as a wrong port rather than silent NaN. Applied to both the Pro dummy
and the execjs-compatible dummy webpack configs for consistency.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: justin808

react_on_rails_pro/spec/dummy/config/webpack/development.js

@@ -13,7 +13,9 @@ const developmentEnvOnly = (clientWebpackConfig, _serverWebpackConfig) => {
         overlay: {
           // bin/dev sets SHAKAPACKER_DEV_SERVER_PORT as a string, which Shakapacker
           // surfaces unchanged on devServer.port. The plugin schema requires a number.
-          sockPort: parseInt(devServer.port, 10),
+          // `|| 3035` falls back to Shakapacker's default if devServer.port is missing,
+          // so a misconfiguration surfaces as a wrong port rather than silent NaN.
+          sockPort: parseInt(devServer.port, 10) || 3035,
         },
       }),
     );

react_on_rails_pro/spec/execjs-compatible-dummy/config/webpack/development.js

@@ -18,7 +18,9 @@ const developmentEnvOnly = (clientWebpackConfig, _serverWebpackConfig) => {
         overlay: {
           // bin/dev sets SHAKAPACKER_DEV_SERVER_PORT as a string, which Shakapacker
           // surfaces unchanged on devServer.port. The plugin schema requires a number.
-          sockPort: parseInt(devServer.port, 10),
+          // `|| 3035` falls back to Shakapacker's default if devServer.port is missing,
+          // so a misconfiguration surfaces as a wrong port rather than silent NaN.
+          sockPort: parseInt(devServer.port, 10) || 3035,
         },
       }),
     );