Make beads claude code skill installable via marketplace (#468)

Reorganize the claude-code-skill into a publishable plugin that can be
installed through the beads-marketplace. Users can now reference the
'beads' skill right after installing the marketplace.

Co-authored-by: Steve Yegge <steve.yegge@gmail.com>

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "beads",
   "description": "AI-supervised issue tracker for coding workflows. Manage tasks, discover work, and maintain context with simple CLI commands.",
-  "version": "0.29.0",
+  "version": "0.30.0",
   "author": {
     "name": "Steve Yegge",
     "url": "https://github.com/steveyegge"