Upgrade to Ruby 4.0.1, bump version to 0.9.0

Replace CGI.parse (removed in Ruby 4.0) with Rack::Utils.parse_query
in application controller, sessions controller, and OIDC tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/initializers/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Clinch
-  VERSION = "0.8.8"
+  VERSION = "0.9.0"
 end