refactor(skills): move skills to canonical top-level skills/ with .claude symlink

Establish a single source of truth for agent skills. The real files now live in
the top-level skills/ directory (the publishing convention used by Vercel,
Supabase, and Cloudflare, and the tree Honcho's `npx skills add` distributes).
.claude/skills becomes a symlink to ../skills so Claude Code discovery keeps
working off the one tree — eliminating the parallel-copy sync burden.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills

@@ -0,0 +1 @@
+../skills