Fix NODE_ENV not being set when running shakapacker-dev-server (#823)

The DevServerRunner class was missing calls to
Shakapacker.ensure_node_env! in both the main run() method and
run_with_build_config() method. This caused NODE_ENV to be undefined
when users ran bin/shakapacker-dev-server, breaking webpack configs that
dynamically require environment-specific files.

This fix ensures NODE_ENV is properly set to match RAILS_ENV (or
"production" by default) before executing the dev server, consistent
with how WebpackRunner and the base Runner class handle environment
initialization.

Fixes #802

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

### Summary

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### Pull Request checklist

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- [ ] Add/update test to cover these changes
- [ ] Update documentation
- [ ] Update CHANGELOG file



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Development server now ensures the Node environment is properly
initialized before starting, preventing potential environment-related
configuration issues.

* **Tests**
* Added verification that NODE_ENV is correctly set to "development"
when required.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Claude <[email protected]>

Author: Seifeldin7

lib/shakapacker/dev_server_runner.rb

@@ -18,6 +18,8 @@ def self.run(argv)
         exit(0)
       end
 
+      Shakapacker.ensure_node_env!
+
       # Check for --build flag
       build_index = argv.index("--build")
       if build_index
@@ -65,6 +67,8 @@ def self.run(argv)
     end
 
     def self.run_with_build_config(argv, build_config)
+      Shakapacker.ensure_node_env!
+
       # Apply build config environment variables
       build_config[:environment].each do |key, value|
         ENV[key] = value.to_s

spec/shakapacker/dev_server_runner_spec.rb

@@ -136,6 +136,37 @@
     end
   end
 
+  describe "NODE_ENV environment variable" do
+    it "sets NODE_ENV when not already set" do
+      original_node_env = ENV.delete("NODE_ENV")
+
+      begin
+        Dir.chdir(test_app_path) do
+          klass = Shakapacker::DevServerRunner
+
+          allow(Shakapacker::Utils::Manager).to receive(:error_unless_package_manager_is_obvious!)
+
+          instance = klass.new([])
+
+          allow(klass).to receive(:new).and_return(instance)
+
+          # Stub build_cmd and system to prevent actual execution
+          allow(instance).to receive(:build_cmd).and_return(["webpack", "serve"])
+          allow(instance).to receive(:system) do |*args|
+            system("true")  # Sets $? to successful status
+            true
+          end
+
+          klass.run([])
+
+          expect(ENV["NODE_ENV"]).to eq("development")
+        end
+      ensure
+        ENV["NODE_ENV"] = original_node_env if original_node_env
+      end
+    end
+  end
+
   private
 
     def verify_command(cmd, argv: [], env: Shakapacker::Compiler.env)