Add Antigravity CLI (agy) to the AI agent list, now that Gemini CLI is enterprise-only

[gpompeo]

Since June 18, 2026, Gemini CLI no longer serves Google AI Pro/Ultra or free-tier requests — it's now scoped to Gemini Code Assist Standard/Enterprise and paid Enterprise Agent Platform API keys (Google's announcement). For everyone but enterprise users, omarchy default agent gemini (bin/omarchy-default-agent) and the setup.default.agent.gemini entry in default/omarchy/omarchy-menu.jsonc now point at a tool most individual users can no longer actually use.

Google's own replacement for individual/free-tier users is Antigravity CLI (binary agy), which is where that gemini traffic is being redirected. Could Omarchy add it as an agent option — either alongside or in place of gemini — in:

• bin/omarchy-default-agent (new antigravity | agy) case)
• the setup.default.agent.* block in omarchy-menu.jsonc

One wrinkle worth flagging: unlike the other agents here, Antigravity CLI isn't distributed as an npm/mise-registry package — it's a Go binary installed via curl -fsSL https://antigravity.google/cli/install.sh | bash (install docs), so the existing mise where "$agent_package" install check in omarchy-default-agent would need a different install path for this one (or an aqua/ubi mise backend if one exists for it) rather than a plain agent_package npm name.

Happy to help test/PR this if useful.