skill_list and skill_load are now external shell scripts (data/tools/).
Removed from builtins: SkillList, SkillLoad, SkillActive.
Removed: toolsrv/skills.go, tools/builtin/skill.go, WithSkillsRegistry,
SkillsRegistry accessor, ListSkillsTools.
ollie-remote no longer initializes a skills registry.
The demarcation: built-ins mutate agent internals (tool schema, context
injection). Skills are just file reads — no special treatment needed.
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