Fix: Properly stub ReactOnRailsPro module with configuration method

Fixed test failures caused by attempting to mock configuration on an
empty Module stub. The stubbed ReactOnRailsPro module now properly
implements the configuration getter/setter methods.

Changes:
- Created proper mock Pro module with working configuration methods
- Set configuration directly instead of using allow().to receive()
- Matches the real Pro gem's module structure

This fixes 4 test failures:
- returns private path when it exists even if public path also exists
- fallbacks to public path when private path does not exist and public path exists
- returns configured path if both private and public paths do not exist
- enforces private RSC bundles and never checks public directory

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

Co-Authored-By: Claude <[email protected]>

Author: AbanoubGhadban

spec/react_on_rails/utils_spec.rb

@@ -247,11 +247,23 @@ def mock_dev_server_running
               before do
                 # Mock Pro gem being available
                 allow(described_class).to receive(:react_on_rails_pro?).and_return(true)
-                stub_const("ReactOnRailsPro", Module.new)
+
+                # Create a mock Pro module with configuration method
+                pro_module = Module.new do
+                  def self.configuration
+                    @configuration
+                  end
+
+                  def self.configuration=(config)
+                    @configuration = config
+                  end
+                end
+                stub_const("ReactOnRailsPro", pro_module)
+
                 pro_config = double("ProConfiguration") # rubocop:disable RSpec/VerifiedDoubles
-                allow(ReactOnRailsPro).to receive(:configuration).and_return(pro_config)
                 allow(pro_config).to receive_messages(rsc_bundle_js_file: rsc_bundle_name,
                                                       react_server_client_manifest_file: nil)
+                ReactOnRailsPro.configuration = pro_config
               end
 
               context "with enforce_private_server_bundles=false" do