Add non-blocking improvements to precompile hook implementation

This commit implements additional safety and robustness improvements
suggested during code review.

Improvements:
- Safer command execution: Use Shellwords.split to prevent shell
  metacharacter interpretation when executing precompile hooks
- Better test isolation: Add after hook to clean up
  SHAKAPACKER_SKIP_PRECOMPILE_HOOK env var even if tests fail
- Updated test mocks: All Open3.capture3 expectations now use split
  arguments matching Shellwords behavior

These changes are non-blocking improvements that enhance code safety
without changing user-facing behavior.

All tests pass (35 examples, 0 failures) and RuboCop is clean (153
files, no offenses).

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

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

Author: justin808

lib/react_on_rails/dev/server_manager.rb

@@ -216,6 +216,7 @@ def run_from_command_line(args = ARGV)
 
         def run_precompile_hook_if_present
           require "open3"
+          require "shellwords"
 
           hook_value = PackerUtils.shakapacker_precompile_hook_value
           return unless hook_value
@@ -228,7 +229,9 @@ def run_precompile_hook_if_present
           puts ""
 
           # Capture stdout and stderr for better error reporting
-          stdout, stderr, status = Open3.capture3(hook_value.to_s)
+          # Use Shellwords.split for safer command execution (prevents shell metacharacter interpretation)
+          command_args = Shellwords.split(hook_value.to_s)
+          stdout, stderr, status = Open3.capture3(*command_args)
 
           if status.success?
             puts Rainbow("✅ Precompile hook completed successfully").green

spec/react_on_rails/dev/server_manager_spec.rb

@@ -276,6 +276,12 @@ def mock_system_calls
       ENV.delete("SHAKAPACKER_SKIP_PRECOMPILE_HOOK")
     end
 
+    after do
+      # Clean up environment variable after each test to ensure test isolation
+      # This ensures cleanup even if tests fail
+      ENV.delete("SHAKAPACKER_SKIP_PRECOMPILE_HOOK")
+    end
+
     context "when precompile hook is configured" do
       before do
         # Default to a version that supports the skip flag (no warning)
@@ -291,7 +297,7 @@ def mock_system_calls
       it "runs the hook and sets environment variable for development mode" do
         status_double = instance_double(Process::Status, success?: true)
         expect(Open3).to receive(:capture3)
-          .with("bundle exec rake react_on_rails:locale")
+          .with("bundle", "exec", "rake", "react_on_rails:locale")
           .and_return(["", "", status_double])
 
         described_class.run_from_command_line([])
@@ -302,7 +308,7 @@ def mock_system_calls
       it "runs the hook and sets environment variable for static mode" do
         status_double = instance_double(Process::Status, success?: true)
         expect(Open3).to receive(:capture3)
-          .with("bundle exec rake react_on_rails:locale")
+          .with("bundle", "exec", "rake", "react_on_rails:locale")
           .and_return(["", "", status_double])
 
         described_class.run_from_command_line(["static"])
@@ -318,7 +324,7 @@ def mock_system_calls
 
         # Expect both Open3.capture3 calls: one for the hook, one for assets:precompile
         expect(Open3).to receive(:capture3)
-          .with("bundle exec rake react_on_rails:locale")
+          .with("bundle", "exec", "rake", "react_on_rails:locale")
           .and_return(["", "", hook_status_double])
         expect(Open3).to receive(:capture3)
           .with(env, *argv)
@@ -332,7 +338,7 @@ def mock_system_calls
       it "exits when hook fails" do
         status_double = instance_double(Process::Status, success?: false)
         expect(Open3).to receive(:capture3)
-          .with("bundle exec rake react_on_rails:locale")
+          .with("bundle", "exec", "rake", "react_on_rails:locale")
           .and_return(["", "", status_double])
         expect_any_instance_of(Kernel).to receive(:exit).with(1)
 
@@ -379,7 +385,7 @@ def mock_system_calls
         it "displays warning about unsupported SHAKAPACKER_SKIP_PRECOMPILE_HOOK" do
           status_double = instance_double(Process::Status, success?: true)
           expect(Open3).to receive(:capture3)
-            .with("bundle exec rake react_on_rails:locale")
+            .with("bundle", "exec", "rake", "react_on_rails:locale")
             .and_return(["", "", status_double])
 
           expect do
@@ -402,7 +408,7 @@ def mock_system_calls
         it "does not display warning" do
           status_double = instance_double(Process::Status, success?: true)
           expect(Open3).to receive(:capture3)
-            .with("bundle exec rake react_on_rails:locale")
+            .with("bundle", "exec", "rake", "react_on_rails:locale")
             .and_return(["", "", status_double])
 
           expect do