fix(update): pass full name@marketplace to claude plugin update

`claude plugin update` rejects a bare plugin name when multiple
marketplaces are registered — the CLI demands `name@marketplace`.
update-all.sh stripped the suffix via `${_p%%@*}`, causing every
marketplace plugin update to fail with "Plugin not found". Fixed
by passing the unmodified spec from `claude plugin list`.

Also adds install + update paths for external skills distributed
through the `npx skills` CLI (vercel-labs/skills):
  - alchaincyf/darwin-skill
  - alchaincyf/find-skills

These land in ~/.agents/skills/ and are now symlinked into
$REPO/skills/ via link.sh using absolute paths — the previous
relative `../../.agents/...` targets resolved incorrectly when
the repo is cloned below $HOME (as ~/Documents/claude/), leaving
dangling symlinks.

Co-Authored-By: Claude <noreply@anthropic.com>

link.sh

@@ -57,6 +57,27 @@ else
   echo "⚠️  emil-design-eng not found — run: make plugin"
 fi
 
+# External skills installed via `npx skills add` live under
+# $HOME/.agents/skills/. We symlink them into $REPO/skills/ with
+# absolute paths so the link stays valid regardless of where the
+# repo is cloned (relative ../../ paths broke on repos deeper than
+# one level below $HOME).
+NPX_EXTERNAL_SKILLS=(darwin-skill find-skills)
+for _ext in "${NPX_EXTERNAL_SKILLS[@]}"; do
+  _target="$HOME/.agents/skills/$_ext"
+  _link="$REPO/skills/$_ext"
+  if [ ! -d "$_target" ]; then
+    echo "⚠️  $_ext not installed at $_target — run: make plugin"
+    continue
+  fi
+  if [ -L "$_link" ] && [ "$(readlink "$_link")" = "$_target" ]; then
+    continue
+  fi
+  rm -f "$_link"
+  ln -sf "$_target" "$_link"
+  CHANGED=$((CHANGED + 1))
+done
+
 if [ "$CHANGED" -eq 0 ]; then
   echo "✅ All symlinks already up to date."
 else