docs: update sandbox image command (google-gemini#26774)

Author: sjhddh

docs/get-started/installation.mdx

@@ -111,8 +111,8 @@ You can also run Gemini CLI using one of the following advanced methods:
     directly. This is useful for environments where you only have Docker and want
     to run the CLI.
     ```bash
-    # Run the published sandbox image
-    docker run --rm -it us-docker.pkg.dev/gemini-code-dev/gemini-cli/sandbox:0.1.1
+    # Run the published sandbox image for a specified CLI version
+    docker run --rm -it us-docker.pkg.dev/gemini-code-dev/gemini-cli/sandbox:0.42.0-nightly.20260428.g59b2dea0e
     ```
   - **Using the `--sandbox` flag:** If you have Gemini CLI installed locally
     (using the standard installation described above), you can instruct it to run