Fix ESLint and formatting issues from PR review

- Fix performance API compatibility with polyfill
- Add missing clientStartup mock in tests
- Replace globalThis with window in test file
- Use async import instead of require
- Add language hints to markdown code blocks
- Ensure files end with newline character

Author: justin808

IMPROVEMENT_SUMMARY.md

@@ -7,6 +7,7 @@ This implementation provides the first step in the React on Rails incremental im
 ## Changes Made
 
 ### 1. SmartError Class (`lib/react_on_rails/smart_error.rb`)
+
 - New intelligent error class that provides contextual help
 - Supports multiple error types:
   - `component_not_registered` - Component registration issues
@@ -22,6 +23,7 @@ This implementation provides the first step in the React on Rails incremental im
   - Shows context-aware troubleshooting steps
 
 ### 2. Enhanced PrerenderError (`lib/react_on_rails/prerender_error.rb`)
+
 - Improved error formatting with colored headers
 - Pattern-based error detection for common issues:
   - `window is not defined` - Browser API on server
@@ -32,6 +34,7 @@ This implementation provides the first step in the React on Rails incremental im
 - Better organization of error information
 
 ### 3. Component Registration Debugging (JavaScript)
+
 - New debug options in `ReactOnRails.setOptions()`:
   - `debugMode` - Full debug logging
   - `logComponentRegistration` - Component registration details
@@ -42,14 +45,17 @@ This implementation provides the first step in the React on Rails incremental im
   - Registration success confirmations
 
 ### 4. Helper Module Updates (`lib/react_on_rails/helper.rb`)
+
 - Integrated SmartError for auto-loaded bundle errors
 - Required smart_error module
 
 ### 5. TypeScript Types (`node_package/src/types/index.ts`)
+
 - Added type definitions for new debug options
 - Documented debug mode and registration logging options
 
 ### 6. Tests
+
 - Ruby tests (`spec/react_on_rails/smart_error_spec.rb`)
   - Tests for each error type
   - Validation of error messages and solutions
@@ -60,6 +66,7 @@ This implementation provides the first step in the React on Rails incremental im
   - Timing information validation
 
 ### 7. Documentation (`docs/guides/improved-error-messages.md`)
+
 - Complete guide on using new error features
 - Examples of each error type
 - Debug mode configuration
@@ -68,6 +75,7 @@ This implementation provides the first step in the React on Rails incremental im
 ## Benefits
 
 ### For Developers
+
 1. **Faster debugging** - Errors now tell you exactly what to do
 2. **Less context switching** - Solutions are provided inline
 3. **Typo detection** - Suggests correct component names
@@ -77,12 +85,14 @@ This implementation provides the first step in the React on Rails incremental im
 ### Examples of Improvements
 
 #### Before:
-```
+
+```text
 Component HelloWorld not found
 ```
 
 #### After (Updated with Auto-Bundling Priority):
-```
+
+```text
 ❌ React on Rails Error: Component 'HelloWorld' Not Registered
 
 Component 'HelloWorld' was not found in the component registry.
@@ -120,23 +130,27 @@ The improved error messages now **prioritize React on Rails' auto-bundling featu
 ## Usage
 
 ### Enable Debug Mode (JavaScript)
+
 ```javascript
 // In your entry file
 ReactOnRails.setOptions({
   debugMode: true,
-  logComponentRegistration: true
+  logComponentRegistration: true,
 });
 ```
 
 ### View Enhanced Errors (Rails)
+
 Errors are automatically enhanced - no configuration needed. For full details:
+
 ```ruby
 ENV["FULL_TEXT_ERRORS"] = "true"
 ```
 
 ## Next Steps
 
 This is Phase 1 of the incremental improvements. Next phases include:
+
 - Enhanced Doctor Command (Phase 1.2)
 - Modern Generator Templates (Phase 2.1)
 - Rspack Migration Assistant (Phase 3.1)
@@ -145,10 +159,11 @@ This is Phase 1 of the incremental improvements. Next phases include:
 ## Testing
 
 Due to Ruby version constraints on the system (Ruby 2.6, project requires 3.0+), full testing wasn't completed, but:
+
 - JavaScript builds successfully
 - Code structure follows existing patterns
 - Tests are provided for validation
 
 ## Impact
 
-This change has **High Impact** with **Low Effort** (2-3 days), making it an ideal first improvement. It immediately improves the developer experience without requiring any migration or configuration changes.
+This change has **High Impact** with **Low Effort** (2-3 days), making it an ideal first improvement. It immediately improves the developer experience without requiring any migration or configuration changes.