fix: stage skills before the change check in sync workflow

[stefanjudis]

Bug

The Commit and push if changed step gated on git diff --quiet skills/. git diff (no --cached) only inspects tracked files, so a brand-new untracked file is invisible to it. The job reported "No skill changes" and exited before git add.

This is deterministic, not a caching/timing issue — re-running never helps. Practical effect: no skill that introduces a new file has ever synced. Only edits and deletions to already-tracked files propagated. (The recently-added playwright skill landed via PR, not the daily job — which is why this went unnoticed.)

Fix

Stage first, then gate on the staged diff (git diff --cached --quiet). The step already ran git add skills/ immediately before committing, so this just moves that line above the guard — the smallest correct change.

git add skills/
if git diff --cached --quiet skills/; then
  echo "No skill changes — nothing to commit."
  exit 0
fi
...
git commit -m "chore: sync skills"
git push

Test plan

• Pre-commit hook (lint/format/typecheck) clean
• Next scheduled run (or a manual workflow_dispatch) commits new files; CI logs confirm the staged-diff gate sees them