Fix external broken links in documentation

Fixed broken external GitHub links:
- Updated shakapacker environment config links from .js to .ts files
- Removed outdated react-webpack-rails-tutorial RouterApp file references
- Fixed README.md advanced-topics link to point to guides/advanced/

All external links now point to valid resources.

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

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

Author: justin808

docs/README.md

@@ -28,7 +28,7 @@ Jump to what you need
 
 - **[Installation Guide](./getting-started/installation-into-an-existing-rails-app.md)** - Detailed setup
 - **[API Reference](./api-reference/README.md)** - Quick lookup
-- **[Advanced Features](./advanced-topics/README.md)** - SSR, Redux, Router
+- **[Advanced Features](./guides/advanced/README.md)** - SSR, Redux, Router
 
 ### 🏗️ **Migrating from Other Solutions**
 

docs/building-features/react-router.md

@@ -24,14 +24,10 @@ const RouterApp = (props, railsContext) => {
 };
 ```
 
-For a fleshed out integration of React on Rails with React Router, check out [React Webpack Rails Tutorial Code](https://github.com/shakacode/react-webpack-rails-tutorial), specifically the files:
+For a fleshed out integration of React on Rails with React Router, check out [React Webpack Rails Tutorial Code](https://github.com/shakacode/react-webpack-rails-tutorial), specifically the routing configuration in:
 
 - [react-webpack-rails-tutorial/client/app/bundles/comments/routes/routes.jsx](https://github.com/shakacode/react-webpack-rails-tutorial/blob/master/client/app/bundles/comments/routes/routes.jsx)
 
-- [react-webpack-rails-tutorial/client/app/bundles/comments/startup/ClientRouterApp.jsx](https://github.com/shakacode/react-webpack-rails-tutorial/blob/master/client/app/bundles/comments/startup/ClientRouterApp.jsx)
-
-- [react-webpack-rails-tutorial/client/app/bundles/comments/startup/ServerRouterApp.jsx](https://github.com/shakacode/react-webpack-rails-tutorial/blob/master/client/app/bundles/comments/startup/ServerRouterApp.jsx)
-
 # Server Rendering Using React Router V4
 
 Your Render-Function may not return an object with the property `renderedHtml`. Thus, you call

docs/core-concepts/webpack-configuration.md

@@ -38,5 +38,5 @@ const { config, devServer } = require('shakapacker');
 
 You will want to consider using some of the same values set in these files:
 
-- https://github.com/shakacode/shakapacker/blob/master/package/environments/base.js
-- https://github.com/shakacode/shakapacker/blob/master/package/environments/development.js
+- https://github.com/shakacode/shakapacker/blob/master/package/environments/base.ts
+- https://github.com/shakacode/shakapacker/blob/master/package/environments/development.ts