refactor(installer): remove dead Antigravity auth plugin code

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>

src/cli/cli-installer.ts

@@ -1,9 +1,7 @@
 import color from "picocolors"
 import type { InstallArgs } from "./types"
 import {
-  addAuthPlugins,
   addPluginToOpenCodeConfig,
-  addProviderConfig,
   detectCurrentConfig,
   getOpenCodeVersion,
   isOpenCodeInstalled,
@@ -45,7 +43,7 @@ export async function runCliInstaller(args: InstallArgs, version: string): Promi
 
   printHeader(isUpdate)
 
-  const totalSteps = 6
+  const totalSteps = 4
   let step = 1
 
   printStep(step++, totalSteps, "Checking OpenCode installation...")
@@ -77,28 +75,6 @@ export async function runCliInstaller(args: InstallArgs, version: string): Promi
     `Plugin ${isUpdate ? "verified" : "added"} ${SYMBOLS.arrow} ${color.dim(pluginResult.configPath)}`,
   )
 
-  const needsProviderSetup = config.hasGemini || config.hasOpenAI || config.hasCopilot
-
-  if (needsProviderSetup) {
-    printStep(step++, totalSteps, "Adding auth plugins...")
-    const authResult = await addAuthPlugins(config)
-    if (!authResult.success) {
-      printError(`Failed: ${authResult.error}`)
-      return 1
-    }
-    printSuccess(`Auth plugins configured ${SYMBOLS.arrow} ${color.dim(authResult.configPath)}`)
-
-    printStep(step++, totalSteps, "Adding provider configurations...")
-    const providerResult = addProviderConfig(config)
-    if (!providerResult.success) {
-      printError(`Failed: ${providerResult.error}`)
-      return 1
-    }
-    printSuccess(`Providers configured ${SYMBOLS.arrow} ${color.dim(providerResult.configPath)}`)
-  } else {
-    step += 2
-  }
-
   printStep(step++, totalSteps, "Writing oh-my-opencode configuration...")
   const omoResult = writeOmoConfig(config)
   if (!omoResult.success) {
@@ -156,7 +132,7 @@ export async function runCliInstaller(args: InstallArgs, version: string): Promi
     printBox(
       `Run ${color.cyan("opencode auth login")} and select your provider:\n` +
         (config.hasClaude ? `  ${SYMBOLS.bullet} Anthropic ${color.gray("→ Claude Pro/Max")}\n` : "") +
-        (config.hasGemini ? `  ${SYMBOLS.bullet} Google ${color.gray("→ OAuth with Antigravity")}\n` : "") +
+        (config.hasGemini ? `  ${SYMBOLS.bullet} Google ${color.gray("→ Gemini")}\n` : "") +
         (config.hasCopilot ? `  ${SYMBOLS.bullet} GitHub ${color.gray("→ Copilot")}` : ""),
       "Authenticate Your Providers",
     )