Sync the fpf-core skill from the canonical FPF-Spec.md monolith.
Use when: (1) the FPF specification has been updated (git pull shows new commits),
(2) the fpf-core skill references/ are stale or show wrong counts,
(3) running scheduled maintenance on LFW skills.
Self-contained — bundles decompose_fpf.py + _common.py directly.
No dependencies on external skills. Works only with the local skill at
`../fpf-core/` (relative to this skill) — NOT the global user skill.
