Fix documentation issues identified in PR review

Addresses valid issues from Claude's PR review:

1. Fixed JavaScript syntax error in using-react-on-rails.md:192
   - Changed semicolon to comma in object destructuring example
   - Was accidentally introduced during linting commit

2. Clarified Rails version requirements in tutorial.md
   - Changed "We support Rails 6 and later" to "This tutorial targets Rails 7.0+"
   - Explicitly noted Rails 6 is supported but tutorial uses Rails 7
   - Removed version confusion between prerequisites and tutorial steps

3. Fixed markdownlint issues
   - Added language hint to code fence in using-react-on-rails.md (text)
   - Added language hint to Procfile code fence in heroku-deployment.md (procfile)

These changes ensure code examples are syntactically correct and version
requirements are clear for users following the tutorial.

Author: ihabadham

docs/deployment/heroku-deployment.md

@@ -97,7 +97,7 @@ Next, configure your app for Puma, per the [instructions on Heroku](https://devc
 
 Create `./Procfile` with the following content. This is what Heroku uses to start your app.
 
-```
+```procfile
 web: bundle exec puma -C config/puma.rb
 ```
 

docs/getting-started/tutorial.md

@@ -49,7 +49,7 @@ By the time you read this, the latest may have changed. Be sure to check the ver
 Trying out **React on Rails** is super easy, so long as you have the basic prerequisites.
 
 - **Ruby:** We support all active Ruby versions but recommend using the latest stable Ruby version. Solutions like [rvm](https://rvm.io) or [rbenv](https://github.com/rbenv/rbenv) make it easy to have multiple Ruby versions on your machine.
-- **Rails:** We support Rails 6 and later.
+- **Rails:** This tutorial targets Rails 7.0+. React on Rails supports Rails 6 and later, but some tutorial steps may differ for Rails 6.
 - **Nodejs:** We support all [active Node versions](https://github.com/nodejs/release#release-schedule) but recommend using the latest LTS release of Nodejs for the longest support. Older inactive node versions might still work but is not guaranteed. We also recommend using [nvm](https://github.com/nvm-sh/nvm/) to ease using different node versions in different projects.
 - **yarn:** We use [yarn classic](https://classic.yarnpkg.com/) as our node package manager.
 - You need to have either [Overmind](https://github.com/DarthSim/overmind) or [Foreman](https://rubygems.org/gems/foreman) as a process manager.
@@ -58,7 +58,7 @@ Trying out **React on Rails** is super easy, so long as you have the basic prere
 
 Then we need to create a fresh Rails application as follows.
 
-First, be sure to run `rails -v` and check you are using Rails 7.0 or above.
+First, be sure to run `rails -v` and check you are using Rails 7.0 or above for this tutorial.
 
 ```bash
 # For Rails 6.x

docs/getting-started/using-react-on-rails.md

@@ -123,7 +123,7 @@ After running `rails generate react_on_rails:install`, you'll see:
 
 ### Component Structure
 
-```
+```text
 app/javascript/
 └── bundles/HelloWorld/          # or src/HelloWorld/ror_components/ with auto-bundling
     └── HelloWorld.jsx
@@ -187,11 +187,13 @@ export default MyApp;
 For advanced server rendering (like React Router), you can return an object:
 
 ```js
-{
+({
   renderedHtml: {
-    componentHtml, redirectLocation, error;
-  }
-}
+    componentHtml,
+    redirectLocation,
+    error,
+  },
+});
 ```
 
 Use with `react_component_hash` helper for multiple HTML strings (useful with React Helmet for meta tags).