chore(skills): drop find-skills — unused, and its update step began timing out

RC fix (soak day 1): `make update` step 7.5 failed on a 300s clone timeout
of alchaincyf/find-skills. The skill (search the skills.sh registry from
Claude) was never used; the discovery case stays reachable manually via
`npx -y skills find <query>`. Removed from install-plugins.sh (install list
+ summary + comment), update-all.sh (refresh list), link.sh
(NPX_EXTERNAL_SKILLS), lib/toggle-external.sh (MANAGED_TOOLS + case arms),
plugin-advisor.md, .gitignore; local skills/find-skills symlink deleted.
Memory-registry and test-fixture mentions kept — append-only history.
toggle-external `list` verified post-removal; suites 8/8.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XpphkdTosUzokBDNG7PToS

update-all.sh

@@ -388,7 +388,6 @@ echo "── Updating external skills (npx skills)..."
 if command -v npx &>/dev/null; then
   NPX_SKILLS=(
     "alchaincyf/darwin-skill"
-    "alchaincyf/find-skills"
   )
   for _src in "${NPX_SKILLS[@]}"; do
     _name="${_src##*/}"