feat: scope npm package as @dietrichgebert/ponytail (#280)

Publish under a scope you own outright instead of opencode-ponytail (which
sits on a third-party npm account). Matches the GitHub handle and repo.
publishConfig.access is already public, which scoped public packages need.

package.json

@@ -1,5 +1,5 @@
 {
-  "name": "opencode-ponytail",
+  "name": "@dietrichgebert/ponytail",
   "version": "4.8.1",
   "description": "Lazy senior dev mode for AI agents. The best code is the code you never wrote.",
   "keywords": ["opencode-plugin", "opencode", "ponytail", "pi-package", "pi", "skills"],