Upgrade Ruby from 3.3.6 to 3.4.1

Updated Ruby to the latest stable 3.4.x release for improved performance
and security updates.

Changes:
- Updated .ruby-version to 3.4.1
- Updated Gemfile ruby version requirement to 3.4.1
- Updated README.md to reflect Ruby 3.4.1 requirement
- Updated Dockerfile from ruby:2.6.5 to ruby:3.4.1
- Removed outdated bundler version constraint in Dockerfile

Tested:
- Bundle install successful with Ruby 3.4.1
- Test suite runs successfully (46 examples, 1 pre-existing failure)
- Rails server starts and responds correctly

Fixes #490

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

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

Dockerfile

@@ -1,9 +1,9 @@
-FROM --platform=linux/amd64 ruby:2.6.5
+FROM --platform=linux/amd64 ruby:3.4.1
 RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
 RUN mkdir /myapp
 WORKDIR /myapp
 ADD Gemfile /myapp/Gemfile
 ADD Gemfile.lock /myapp/Gemfile.lock
-RUN gem install bundler -v 1.17.3
+RUN gem install bundler
 RUN bundle install
 ADD . /myapp