## What happens

Setup → Defaults → Agent → **Gemini** installs `gemini` via mise, writes it as
the default agent, and launches it — but the CLI can no longer authenticate.
Signing in with Google completes normally in the browser (the CLI even appears
in the account's authorized apps), then the terminal fails with:

```
Failed to sign in. Message: This client is no longer supported for Gemini Code
Assist for individuals. To continue using Gemini, please migrate to the
Antigravity suite of products: https://antigravity.google
```

This isn't a stale-version problem — reproduced on gemini-cli 0.56.0, the
current release. On 2026-06-18 Google stopped serving Gemini CLI requests for
all individual accounts (free tier, Google AI Pro, and Ultra), and withdrew the
"Login with Google" OAuth path for them. Gemini CLI now works only with a paid
API key or an enterprise licence. Announcement:
https://developers.googleblog.com/an-important-update-transitioning-gemini-cli-to-antigravity-cli/

So the menu entry is a dead end for every individual user: it silently installs
a package, sets it as the system default agent, and leaves the user with an
agent that cannot start. `SUPER + SHIFT + CTRL + A` then launches a CLI that
immediately fails to sign in.

## Steps to reproduce

1. Sign in to a personal Google account (free, AI Pro, or Ultra — not enterprise).
2. Open the Omarchy menu → Setup → Defaults → Agent → Gemini.
3. Let it install and launch.
4. Choose "Login with Google" and complete the browser flow.
5. The browser flow succeeds; the CLI prints the error above and exits.

## Expected

Either the Gemini entry is gated on an auth method that still works, or it is
replaced by Google's supported successor.

## Suggested fix

Replace Gemini with **Antigravity CLI** (`agy`), Google's designated
replacement. It keeps Google-account sign-in for individual tiers, so it is a
drop-in for what the Gemini entry used to provide. It is in the mise registry
as `agy` (`aqua:google-antigravity/antigravity-cli`), so the existing
lazy-install path works unchanged.

Three places need an entry:

`bin/omarchy-default-agent`
```bash
agy | antigravity) agent="agy"; name="Antigravity" ;;
```

`bin/omarchy-agent`
```bash
agy)
  command=(agy --dangerously-skip-permissions)
  [[ -n ${prompt:-} ]] && command+=(--prompt-interactive "$prompt")
  ;;
```

`default/omarchy/omarchy-menu.jsonc`
```jsonc
"setup.default.agent.antigravity": {"icon":"󱓞","label":"Antigravity","checked":"[[ \"$(omarchy-default-agent)\" == \"agy\" ]]","action":"omarchy-default-agent agy"},
```

`--dangerously-skip-permissions` is agy's equivalent of the `--yolo` currently
passed to gemini, and `--prompt-interactive` carries over unchanged, so the
unattended-launch behaviour from #6729 is preserved.

Happy to open a PR if that shape looks right.

## System

- Omarchy: 4.0.0-1
- Kernel: 7.1.8-arch1-3
- Hyprland: 0.56.2
- CPU: Intel Core i7-10510U
- GPU: Intel CometLake-U GT2 [UHD Graphics]
- gemini-cli: 0.56.0 (installed via mise by the menu entry itself)