remove gemini cli and antigravity support

packages/coding-agent/src/cli/args.ts

@@ -329,7 +329,6 @@ ${chalk.bold("Environment Variables:")}
   PI_OFFLINE                       - Disable startup network operations when set to 1/true/yes
   PI_TELEMETRY                     - Override install telemetry when set to 1/true/yes or 0/false/no
   PI_SHARE_VIEWER_URL              - Base URL for /share command (default: https://pi.dev/session/)
-  PI_AI_ANTIGRAVITY_VERSION        - Override Antigravity User-Agent version (e.g., 1.23.0)
 
 ${chalk.bold("Built-in Tool Names:")}
   read   - Read file contents

packages/coding-agent/src/core/model-resolver.ts

@@ -19,8 +19,6 @@ export const defaultModelPerProvider: Record<KnownProvider, string> = {
 	"openai-codex": "gpt-5.5",
 	deepseek: "deepseek-v4-pro",
 	google: "gemini-3.1-pro-preview",
-	"google-gemini-cli": "gemini-3.1-pro-preview",
-	"google-antigravity": "gemini-3.1-pro-high",
 	"google-vertex": "gemini-3.1-pro-preview",
 	"github-copilot": "gpt-5.4",
 	openrouter: "moonshotai/kimi-k2.6",