fix: remove automatic antigravity plugin installation

Remove the automatic installation of opencode-antigravity-auth plugin
when users have Gemini configured. This change addresses several issues:

1. Antigravity plugin is causing Google account bans for users
2. Users are unaware the plugin was auto-installed
3. Google has built-in OAuth for Gemini that doesn't require third-party plugins

Users who need the antigravity plugin can manually add it to their
plugin configuration if desired.

Fixes issues with unexpected plugin installation and account safety.

src/cli/config-manager/auth-plugins.ts

@@ -50,13 +50,8 @@ export async function addAuthPlugins(config: InstallConfig): Promise<ConfigMerge
     const rawPlugins = existingConfig?.plugin
     const plugins: string[] = Array.isArray(rawPlugins) ? rawPlugins : []
 
-    if (config.hasGemini) {
-      const version = await fetchLatestVersion("opencode-antigravity-auth")
-      const pluginEntry = version ? `opencode-antigravity-auth@${version}` : "opencode-antigravity-auth"
-      if (!plugins.some((p) => p.startsWith("opencode-antigravity-auth"))) {
-        plugins.push(pluginEntry)
-      }
-    }
+    // Note: opencode-antigravity-auth plugin auto-installation has been removed
+    // Users can manually add auth plugins if needed
 
     const newConfig = { ...(existingConfig ?? {}), plugin: plugins }