Add VTL migration skill and comprehensive migration guide

[adrianjm-dotCMS]

This pull request introduces a comprehensive skill definition for migrating DotCMS VTL custom field templates from legacy Dojo/Dijit APIs to the modern DotCustomFieldApi. The documentation provides clear migration rules, a step-by-step checklist, and a standardized three-file output pattern to ensure safe coexistence of old and new editor modes.

Migration process and rules:

• Added a detailed migration guide in .claude/skills/vtl-migration/SKILL.md, including a quick reference table mapping deprecated Dojo/Dijit API calls to their modern equivalents in DotCustomFieldApi.
• Defined a step-by-step migration process, emphasizing full file understanding, deprecated pattern identification, wrapping logic in DotCustomFieldApi.ready(), and preserving business logic and VTL variables.

Three-file output pattern:

• Established a mandatory three-file output for each migration: the original unchanged file (_old.vtl), the fully migrated file (_new.vtl), and a router file with conditional parsing for legacy and new edit modes.

Code and template migration examples:

• Provided practical code snippets and migration patterns for field references, event handling, dialog migration, and combining multiple onChange handlers.

Quality and verification checklist:

• Included a detailed checklist to ensure all migration requirements are met, such as removal of deprecated APIs

resolves #34450

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[Copilot]

Pull request overview

This pull request introduces a comprehensive VTL (Velocity Template Language) migration skill for GitHub Copilot Code that helps developers migrate DotCMS custom field templates from legacy Dojo/Dijit APIs to the modern DotCustomFieldApi. The skill includes detailed migration rules, a step-by-step checklist, complete code examples, and establishes a standardized three-file output pattern for safe coexistence of old and new editor modes.

Changes:

• Added .claude/skills/vtl-migration/SKILL.md defining the skill metadata, quick reference API mapping table, migration process, three-file output pattern, and quality checklist
• Added .claude/skills/vtl-migration/references/migration-guide.md providing comprehensive migration rules (11 rules), best practices, common pitfalls, special cases, and three complete end-to-end migration examples

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
.claude/skills/vtl-migration/SKILL.md	Skill definition with metadata, quick API reference table, migration process overview, three-file output pattern explanation, and verification checklist
.claude/skills/vtl-migration/references/migration-guide.md	Comprehensive 892-line migration guide covering DotCustomFieldApi introduction, 11 detailed migration rules with code examples, best practices, step-by-step checklist, common pitfalls, special cases, and three complete real-world migration examples