Fix plugin loading: move @opencode-ai/plugin to dependencies (#48)

* 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

* Pin @opencode-ai/plugin version with comment explaining npm plugin loading

- Changed @opencode-ai/plugin from devDependencies to dependencies
- Pinned version to ~1.3.13 (patch updates only)
- Added inline comment explaining why: opencode downloads npm plugins
  without devDependencies, causing module resolution failures
- Kept peerDependency for documentation purposes

* Remove JSON comments and regenerate package-lock.json

- Comments are not valid in JSON, causing manifest to be invalid
- Regenerated package-lock.json to match ~1.3.13 version range

Author: hakanai3d