docs: rename Codex marketplace to data-cloud-plugins (#127)

Author: helloeve

README.md

@@ -160,21 +160,21 @@ _(Tip: Run `/plugin list` inside Claude Code to verify the plugin is active, or
 **1. Install marketplace:**
 
 ```bash
-codex plugin marketplace add GoogleCloudPlatform/data-agent-kit
+codex plugin marketplace add GoogleCloudPlatform/data-cloud-plugins
 ```
 
 **2. Install the plugin:**
 
 ```bash
-codex plugin add cloud-sql-sqlserver@data-agent-kit
+codex plugin add cloud-sql-sqlserver@data-cloud-plugins
 ```
 
 **3. Set env vars:**
 Enter your environment vars as described in the [configuration section](#configuration).
 
 **4. (Optional) Update the marketplace:**
 ```sh
-codex plugin marketplace upgrade data-agent-kit
+codex plugin marketplace upgrade data-cloud-plugins
 ```
 
 </details>