docs: Add Antigravity connection steps for Looker (#2192)

## Description

This PR adds a new section to the `looker_mcp.md` document that explains
how to connect Looker to Antigravity.

The new **"Connect with Antigravity"** section provides two methods for
connecting:

- **MCP Store:** A straightforward method using the built-in MCP Store
in Antigravity.
- **Custom config:** For connecting to a custom MCP server by adding a
configuration to the mcp_config.json file.

These changes will help users easily connect Looker to Antigravity.

## PR Checklist

> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [x] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [x] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [x] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

Co-authored-by: Averi Kitsch <akitsch@google.com>

docs/en/how-to/connect-ide/looker_mcp.md

@@ -18,6 +18,7 @@ to expose your developer assistant tools to a Looker instance:
 * [Cline][cline] (VS Code extension)
 * [Claude desktop][claudedesktop]
 * [Claude code][claudecode]
+* [Antigravity][antigravity]
 
 [toolbox]: https://github.com/googleapis/genai-toolbox
 [gemini-cli]: #configure-your-mcp-client
@@ -27,6 +28,7 @@ to expose your developer assistant tools to a Looker instance:
 [cline]: #configure-your-mcp-client
 [claudedesktop]: #configure-your-mcp-client
 [claudecode]: #configure-your-mcp-client
+[antigravity]: #connect-with-antigravity
 
 ## Set up Looker
 
@@ -38,6 +40,55 @@ to expose your developer assistant tools to a Looker instance:
    listening at a different port, and you will need to use
    `https://looker.example.com:19999` instead.
 
+## Connect with Antigravity
+
+You can connect Looker to Antigravity in the following ways:
+
+* Using the MCP Store
+* Using a custom configuration
+
+{{< notice note >}}
+You don't need to download the MCP Toolbox binary to use these methods.
+{{< /notice >}}
+
+{{< tabpane text=true >}}
+{{% tab header="MCP Store" lang="en" %}}
+The most straightforward way to connect to Looker in Antigravity is by using the built-in MCP Store.
+
+1. Open Antigravity and open the editor's agent panel.
+1. Click the **"..."** icon at the top of the panel and select **MCP Servers**.
+1. Locate **Looker** in the list of available servers and click Install.
+1. Follow the on-screen prompts to securely link your accounts where applicable.
+
+After you install Looker in the MCP Store, resources and tools from the server are automatically available to the editor. 
+
+{{% /tab %}}
+{{% tab header="Custom config" lang="en" %}}
+ To connect to a custom MCP server, follow these steps:
+
+1. Open Antigravity and navigate to the MCP store using the **"..."** drop-down at the top of the editor's agent panel.
+1. To open the **mcp_config.json** file, click **MCP Servers** and then click **Manage MCP Servers > View raw config**.
+1. Add the following configuration, replace the environment variables with your values, and save.
+    
+    ```json
+    {
+      "mcpServers": {
+        "looker": {
+          "command": "npx",
+          "args": ["-y", "@toolbox-sdk/server", "--prebuilt", "looker", "--stdio"],
+          "env": {
+              "LOOKER_BASE_URL": "https://looker.example.com",
+              "LOOKER_CLIENT_ID": "your-client-id",
+              "LOOKER_CLIENT_SECRET": "your-client-secret"
+          }
+        }
+      }
+    }
+    ```
+
+{{% /tab %}}
+{{< /tabpane >}}
+
 ## Install MCP Toolbox
 
 1. Download the latest version of Toolbox as a binary. Select the [correct