* fix: Update Dolibarr Development Best Practices documentation
Updated the Dolibarr Development Best Practices documentation to include core principles, security guidelines, code structure, and workflow guidance. Added detailed sections on database interaction, module development, testing, and reference material. Removed outdated information and improved clarity and organization.
* Update SKILL.md to remove GETPOSTALPHA reference
Removed mention of GETPOSTALPHA shorthand from best practices.
* Qual: Correct extrafields documentation and code examples
Updated SKILL.md with improved extrafields documentation and code examples. The changes include:
- Simplified extrafields loading and access, removed unnecessary code
- Correcte field creation code
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Co-authored-by: Laurent Destailleur <eldy@destailleur.fr>