docs: update shell base image references

Custom workload instructions referenced shell template images that are no longer refreshed. Use the published shell base images and distinguish them from the shell kit.

content/guides/mistral-vibe-sandbox.md

@@ -94,11 +94,11 @@ mistral-vibe/
 └── vibe.dockerfile
 ```
 
-Create `mistral-vibe/vibe.dockerfile`. The `shell-docker` template supplies
+Create `mistral-vibe/vibe.dockerfile`. The `shell-docker-image` base image supplies
 the agent account, Python, `uv`, and the sandbox's Docker tooling:
 
 ```dockerfile {title="mistral-vibe/vibe.dockerfile"}
-FROM docker/sandbox-templates:shell-docker
+FROM docker.io/sbx/shell-docker-image:latest
 
 ARG VIBE_VERSION
 

content/manuals/ai/sandboxes/customize/author/base-images.md

@@ -41,7 +41,11 @@ templates also include a C/C++ compiler toolchain for building native code.
 | `gemini`              | [Gemini CLI](https://github.com/google-gemini/gemini-cli)            |
 | `kiro`                | [Kiro](https://kiro.dev)                                             |
 | `opencode`            | [OpenCode](https://opencode.ai)                                      |
-| `shell`               | No agent pre-installed. Use for manual agent setup.                  |
+
+For a base image without a pre-installed agent, use
+`docker.io/sbx/shell-image:latest`, or
+`docker.io/sbx/shell-docker-image:latest` for Docker Engine inside the sandbox.
+These are base images, separate from the `sbx/shell` kit.
 
 ## Use an image in a v3 workload
 

content/manuals/ai/sandboxes/customize/kits-v2.md

@@ -303,7 +303,7 @@ The agent's container image must provide:
 - HTTP proxy environment variables (`HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY`) preserved across sudo.
 - The agent binary, either baked in or installed with [`setup.install`](#setup).
 
-Build on top of `docker/sandbox-templates:shell-docker` to get these base
+Build on top of `docker.io/sbx/shell-docker-image:latest` to get these base
 requirements.
 
 ## Agent instructions