Fix Ruby version mismatch between Gemfile and .ruby-version

Update both files to use Ruby 3.4.3 to match the installed version and resolve
bundle install failures in CI.

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

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

Author: justin808

.ruby-version

@@ -1 +1 @@
-3.4.6
+3.4.3

Gemfile

@@ -3,7 +3,7 @@
 source "https://rubygems.org"
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby "3.3.7"
+ruby "3.4.3"
 
 gem "react_on_rails", "16.2.0.beta.8"
 gem "shakapacker", "9.3.4.beta.0"