Fix shakapacker gem/npm version mismatch

Update both gem and npm package to shakapacker 9.4.0 to fix CI failures
caused by version mismatch between gem (9.3.4.beta.0) and npm (9.3.3).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: justin808

Gemfile

@@ -6,7 +6,7 @@ git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 ruby "3.4.6"
 
 gem "react_on_rails", "16.2.0.beta.20"
-gem "shakapacker", "9.3.4.beta.0"
+gem "shakapacker", "9.4.0"
 
 # Bundle edge Rails instead: gem "rails", github: "rails/rails"
 gem "listen"

package.json

@@ -92,7 +92,7 @@
     "sass": "^1.58.3",
     "sass-loader": "^13.3.2",
     "sass-resources-loader": "^2.2.5",
-    "shakapacker": "9.3.3",
+    "shakapacker": "9.4.0",
     "stimulus": "^3.0.1",
     "style-loader": "^3.3.1",
     "swc-loader": "^0.2.6",

yarn.lock

@@ -9135,10 +9135,10 @@ setprototypeof@1.2.0:
   resolved "https://registry.npmjs.org/setprototypeof/-/setprototypeof-1.2.0.tgz"
   integrity sha512-E5LDX7Wrp85Kil5bhZv46j8jOeboKq5JMmYM3gVGdGH8xFpPWXUMsNrlODCrkoxMEeNi/XZIwuRvY4XNwYMJpw==
 
-shakapacker@9.3.3:
-  version "9.3.3"
-  resolved "https://registry.npmjs.org/shakapacker/-/shakapacker-9.3.3.tgz#aed2070eb6136f75cf3e92ace740764bacefc7de"
-  integrity sha512-u2SSKb2d1wgMqcvUcg2XT1h9rJzHvGBssFnTO/gvTz3mvnrJAL71A6CVGSDe25gcOkt6TpeBDCxqfaKBXtjJnw==
+shakapacker@9.4.0:
+  version "9.4.0"
+  resolved "https://registry.npmjs.org/shakapacker/-/shakapacker-9.4.0.tgz#a47120208a0433159740a5ba45f8b4736999f9b8"
+  integrity sha512-Kf5+LADw5kkaPHqXDA6NknGt6p8MK9jjWuiudM+ESHcF/POxFZ1S5p7lMsyezvuMRMm0HrltQCM/NPadGEEnVg==
   dependencies:
     js-yaml "^4.1.0"
     path-complete-extname "^1.0.0"