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.

.opencode/plugins/ponytail.mjs

@@ -7,7 +7,7 @@
 // source of truth.
 //
 // OpenCode loads this as a server plugin — add it to your opencode.json:
-//   { "plugin": ["opencode-ponytail"] }
+//   { "plugin": ["@dietrichgebert/ponytail"] }
 
 import { createRequire } from 'module';
 import fs from 'fs';

README.md

@@ -157,7 +157,7 @@ pi install git:github.com/DietrichGebert/ponytail
 Add to `opencode.json`:
 
 ```json
-{ "plugin": ["opencode-ponytail"] }
+{ "plugin": ["@dietrichgebert/ponytail"] }
 ```
 
 Run from a checkout instead (the plugin reuses `hooks/` and `skills/`):

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"],