Sync Plugin Cache Skill (project-local)

Synchronizes the Claude Code plugin cache at ~/.claude/plugins/cache/plan-marshall/ from the multi-target generator output at target/claude/. The pipeline is:

marketplace/bundles/  →  target/claude/  →  ~/.claude/plugins/cache/plan-marshall/{bundle}/{version}/

The middle hop (target/claude/) is produced by the project:finalize-step-deploy-target finalize step or by an explicit python3 marketplace/targets/generate.py --target claude --output target/claude invocation. This skill consumes that output as its source of truth — it does NOT rsync directly from marketplace/bundles/.