Fix plugin loading: move @opencode-ai/plugin to dependencies

- Moved @opencode-ai/plugin from devDependencies to dependencies
  This was causing 'Cannot find module @opencode-ai/plugin' errors
  when the plugin was installed via npm/bun without devDependencies

- The export format remains 'export default plugin' as originally intended
  by the package author

Author: hakanai3d

package-lock.json

@@ -70,6 +70,7 @@
     ]
   },
   "dependencies": {
+    "@opencode-ai/plugin": "^1.3.13",
     "chokidar": "^5.0.0",
     "ignore": "^7.0.5",
     "p-queue": "^9.1.1",
@@ -80,7 +81,6 @@
     "@eslint/js": "^9.39.4",
     "@modelcontextprotocol/sdk": "^1.29.0",
     "@napi-rs/cli": "^3.6.0",
-    "@opencode-ai/plugin": "^1.3.13",
     "@types/node": "^25.5.2",
     "@vitest/coverage-v8": "^4.1.2",
     "eslint": "^9.39.4",