Modernize Gemfile: Jekyll 4.4 + Ruby 3.3 compatibility (fix DO build)

Gemfile

@@ -1,21 +1,11 @@
 source "https://rubygems.org"
-ruby RUBY_VERSION
 
-# Hello! This is where you manage which Jekyll version is used to run.
-# When you want to use a different version, change it below, save the
-# file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
-#
-#     bundle exec jekyll serve
-#
-# This will help ensure the proper Jekyll version is running.
-# Happy Jekylling!
-gem "jekyll", "3.2.0.pre.beta1"
+ruby ">= 3.3.0"
 
-# If you want to use GitHub Pages, remove the "gem "jekyll"" above and
-# uncomment the line below. To upgrade, run `bundle update github-pages`.
-# gem "github-pages", group: :jekyll_plugins
+# Jekyll for static site build
+gem "jekyll", "~> 4.4"
 
-# If you have any plugins, put them here!
-# group :jekyll_plugins do
-#   gem "jekyll-github-metadata", "~> 1.0"
-# end
+# Required dependencies for Ruby 3.3+ compatibility
+gem "rexml"
+gem "base64"
+gem "bigdecimal"