Rename root source directory from src/ to source/ and update all
references in Makefile, manifest.xml, .gitignore, CI workflows,
and wiki documentation. Internal Joomla namespace paths (src/Extension)
are unchanged as they are plugin-internal structure.
CI workflows updated to check source/ first with src/ fallback for
backward compatibility across repos.
Authored-by: Moko Consulting
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>