The validate-workflow task was accidentally deleted during the
XML-to-native-skill refactor in #1864. The schema, handler, and
test fixtures still reference it, creating broken invocations.
Recreates the task as a native skill directory following the
established pattern (SKILL.md + bmad-skill-manifest.yaml + workflow.md),
with the original validation logic preserved.
Fixes#1530
Nikolas de Hor