Document Docker image variants for sandbox-sdk

Add documentation for lean and Python image variants introduced in
cloudflare/sandbox-sdk#259. This breaking change splits the base image
into two variants optimized for different workloads.

- Document default (lean) image without Python (~600-800MB)
- Document Python image with data science packages (~1.3GB)
- Add migration guide for users upgrading from 0.5.5 to 0.5.6+
- Document PYTHON_NOT_AVAILABLE error and how to resolve it
- Update all Dockerfile examples to use 0.5.6 versions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: github-actions[bot]

src/content/docs/sandbox/api/interpreter.mdx

@@ -37,6 +37,26 @@ const ctx = await sandbox.createCodeContext({
 ```
 </TypeScriptExample>
 
+:::caution[Python requires the Python image]
+Creating a Python context requires the `-python` Docker image variant. The default lean image only supports JavaScript and TypeScript.
+
+If you attempt to create a Python context without the Python image, you will receive a `PYTHON_NOT_AVAILABLE` error with HTTP status 501:
+
+<TypeScriptExample>
+```
+try {
+  const ctx = await sandbox.createCodeContext({ language: 'python' });
+} catch (error) {
+  // SandboxError: Python is not available in this container image.
+  // Use the cloudflare/sandbox:<version>-python image variant.
+  console.error(error.message);
+}
+```
+</TypeScriptExample>
+
+To fix this, update your Dockerfile to use the Python image variant. Refer to [Dockerfile reference](/sandbox/configuration/dockerfile/) for migration instructions.
+:::
+
 ### `runCode()`
 
 Execute code in a context and return the complete result.

src/content/docs/sandbox/configuration/dockerfile.mdx

@@ -16,7 +16,7 @@ The Sandbox SDK provides two image variants optimized for different use cases:
 Optimized for shell commands and JavaScript/TypeScript execution (~600-800MB):
 
 ```dockerfile
-FROM docker.io/cloudflare/sandbox:0.3.3
+FROM docker.io/cloudflare/sandbox:0.5.6
 ```
 
 **What's included:**
@@ -31,7 +31,7 @@ FROM docker.io/cloudflare/sandbox:0.3.3
 Full image with Python and data science packages (~1.3GB):
 
 ```dockerfile
-FROM docker.io/cloudflare/sandbox:0.3.3-python
+FROM docker.io/cloudflare/sandbox:0.5.6-python
 ```
 
 **What's included (in addition to default image):**
@@ -46,7 +46,7 @@ Using the lean image reduces image size by ~500MB and improves cold start times.
 :::
 
 :::caution[Version synchronization required]
-Always match the Docker image version to your npm package version. If you're using `@cloudflare/sandbox@0.3.3`, use `docker.io/cloudflare/sandbox:0.3.3` (or `0.3.3-python`) as your base image.
+Always match the Docker image version to your npm package version. If you're using `@cloudflare/sandbox@0.5.6`, use `docker.io/cloudflare/sandbox:0.5.6` (or `0.5.6-python`) as your base image.
 
 **Why this matters**: The SDK automatically checks version compatibility on startup. Mismatched versions can cause features to break or behave unexpectedly. If versions don't match, you'll see warnings in your logs.
 
@@ -59,7 +59,7 @@ Create a `Dockerfile` in your project root:
 
 ```dockerfile title="Dockerfile"
 # Use Python variant if you need Python packages
-FROM docker.io/cloudflare/sandbox:0.3.3-python
+FROM docker.io/cloudflare/sandbox:0.5.6-python
 
 # Install additional Python packages
 RUN pip install --no-cache-dir \
@@ -98,7 +98,7 @@ Run services automatically when the container starts by creating a custom startu
 
 ```dockerfile title="Dockerfile"
 # Choose appropriate variant (default or -python)
-FROM docker.io/cloudflare/sandbox:0.3.3
+FROM docker.io/cloudflare/sandbox:0.5.6
 
 COPY my-app.js /workspace/my-app.js
 COPY startup.sh /workspace/startup.sh
@@ -146,7 +146,7 @@ If you attempt to execute Python code without the `-python` variant, you will re
 
 ## Related resources
 
-- [Image Management](/containers/platform-details/image-management/) - Building and pushing images to Cloudflare\'s registry
+- [Image Management](/containers/platform-details/image-management/) - Building and pushing images to Cloudflare's registry
 - [Wrangler configuration](/sandbox/configuration/wrangler/) - Using custom images in wrangler.jsonc
 - [Docker documentation](https://docs.docker.com/reference/dockerfile/) - Complete Dockerfile syntax
 - [Container concepts](/sandbox/concepts/containers/) - Understanding the runtime environment