Sync Skills from mattpocock/skills

Periodic upstream sync: check https://github.com/mattpocock/skills for new or changed skills, classify each against tunan's existing coverage, translate format conventions, write adapted SKILL.md files, and advance the stored baseline. Run this on a recurring cadence — it is designed to be the single entry point for keeping tunan in sync with mattpocock's skill catalog.

Core Loop

The primary workflow is the periodic delta sync:

--diff  →  review changed skills  →  sync selected  →  advance baseline

1. --diff: Compare mattpocock main HEAD against the stored baseline SHA. List every skill that is new, modified, or deleted since the baseline.
2. Review: Present the delta. The user picks which skills to sync.
3. Sync: For each selected skill, classify → translate → write → README update.
4. Advance baseline: Record the new mattpocock HEAD SHA so the next --diff starts from here.

A single-skill sync (#$ARGUMENTS is a name) also advances the baseline for that skill's category — it records which commit was current when the skill was synced. Bulk --audit does not advance the baseline (it's a discovery tool, not a sync action).