Fix technical issues and improve consistency

- Correct README chapter links to match actual filenames
- Fix Modern::Perl version from invalid '2023' to valid '2018'
- Ensure all code examples use proper Perl syntax and best practices
- Maintain consistency across all chapters

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

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

02-getting-started-modern-perl-setup.md

@@ -141,7 +141,7 @@ Let's write a simple script using modern Perl features. Create a file called `he
 
 ```perl
 #!/usr/bin/env perl
-use Modern::Perl '2023';
+use Modern::Perl '2018';
 use feature 'signatures';
 no warnings 'experimental::signatures';
 
@@ -299,7 +299,7 @@ Here's a typical workflow for developing Perl scripts in 2025:
 1. **Start with a shebang and Modern::Perl**
    ```perl
    #!/usr/bin/env perl
-   use Modern::Perl '2023';
+   use Modern::Perl '2018';
    ```
 
 2. **Write your code**