Fix version compatibility matrix to match gemspec

Update minimum versions to reflect actual gem requirements:
- Ruby: 3.0 (not 3.2)
- Node.js: 18 (not 20)
- Shakapacker: 6.0 (not 8.2.0)
- Rails: 5.2 (not 6.1)

Add note clarifying that CI tests against higher versions but
the gem supports the lower versions shown.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

docs/upgrading/release-notes/16.1.0.md

@@ -28,11 +28,13 @@ Then run `bundle install` and your package manager's install command.
 
 | Component   | Minimum | Recommended |
 | ----------- | ------- | ----------- |
-| Ruby        | 3.2     | 3.3+        |
-| Node.js     | 20      | 22+         |
-| Shakapacker | 8.2.0   | 8.2.0+      |
+| Ruby        | 3.0     | 3.3+        |
+| Node.js     | 18      | 22+         |
+| Shakapacker | 6.0     | 8.2.0+      |
 | React       | 18      | 18+         |
-| Rails       | 6.1     | 7.0+        |
+| Rails       | 5.2     | 7.0+        |
+
+**Note:** CI tests against Ruby 3.2+ and Node.js 20+, but the gem supports lower versions as shown above.
 
 ## New Features in v16.1.0