Fixes#30. OpenCode's plugin loader treats subpath exports like
"oh-my-opencode/google-auth" as separate npm packages, causing
BunInstallFailedError.
Solution: Enable Google auth via `google_auth: true` in
oh-my-opencode.json instead of a separate subpath plugin.
🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)
- Add Zod schema for oh-my-opencode.json configuration validation
- Generate JSON Schema at build time for IDE autocompletion
- Add safeParse validation with error reporting on config load
- Export OhMyOpenCodeConfigSchema for programmatic usage
- Add build:schema script and ./schema.json export
- Update README with $schema usage documentation
