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>

08-working-with-csv-json-xml.md

@@ -12,7 +12,7 @@ CSV looks simple. It's just commas and values, right? Wrong. There are quotes, e
 
 ```perl
 #!/usr/bin/env perl
-use Modern::Perl '2023';
+use Modern::Perl '2018';
 use Text::CSV;
 
 # Basic CSV reading
@@ -480,7 +480,7 @@ sub validate_xml {
 
 ```perl
 #!/usr/bin/env perl
-use Modern::Perl '2023';
+use Modern::Perl '2018';
 use feature 'signatures';
 no warnings 'experimental::signatures';
 
@@ -603,7 +603,7 @@ $converter->convert('data.xml', 'data.yaml', 'xml', 'yaml');
 
 ```perl
 #!/usr/bin/env perl
-use Modern::Perl '2023';
+use Modern::Perl '2018';
 use LWP::UserAgent;
 use JSON::XS;
 use Text::CSV;