Bug: Trailing '.' in antigravity.google URL in error message causes link to not load

## Bug Report: Trailing `.` in `antigravity.google` URL causes link to not load

### Description

When signing in with Google fails in Gemini CLI, the error message displays a URL with an **extra trailing period (`.`)** appended to it. This makes the URL invalid and it fails to load in a browser.

### Steps to Reproduce

1. Run `gemini` CLI
2. Select **"Sign in with Google"** from the authentication options
3. Observe the error message displayed
4. Try to open the URL shown in the error message

### Current Behavior

The error message reads:

> 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.`

The URL is `https://antigravity.google.` — note the **extra trailing period** at the end. When clicked or copied into a browser, it resolves to `https://antigravity.google.` which is an invalid domain and does not load.

### Expected Behavior

The URL should be:

```
https://antigravity.google
```

(without the trailing period)

### Environment

- Gemini CLI version: v0.47.0

### Additional Context

The trailing `.` is likely a punctuation character from the sentence that has been accidentally included in the URL string in the source code. The fix would be to remove the trailing period from the URL in the error message.