The installer was writing Antigravity provider config and calling a no-op addAuthPlugins function. Since opencode-antigravity-auth is no longer auto-installed and OpenCode supports native Google/Gemini auth, all Antigravity-related installer code is dead. Gemini detection now checks for native google provider instead.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
