Deprecate skills without breaking workspaces

Publish deprecation notice and migrate users to replacement skill

Skill publishers managing breaking changes and version upgrades across distributed user bases.

• · deprecated_skill_id
• · replacement_skill_id
• · migration_guide_url

• · deprecation_announcement
• · user_migration_log

• · replacement skill exists and is stable
• · user base identified

• · users on old versions do not auto-update
• · no rollback path for incompatible migrations

• · migration guide required
• · replacement skill link validated