docs: Enhance HumanInTheLoopMiddleware configuration for email review (#1205)

## Overview
The current config produces an issue:

```
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
  File "/home/mc/.venv-langchain-v1/lib/python3.10/site-packages/langchain/agents/middleware/human_in_the_loop.py", line 193, in __init__
    elif tool_config.get("allowed_decisions"):
AttributeError: 'str' object has no attribute 'get'

```

The old example conflicts with the configuration options described in
[LangChain’s
documentation](https://docs.langchain.com/oss/python/langchain/middleware#human-in-the-loop)

The description field is part of InterruptOnConfig, so the dictionary
value should be an InterruptOnConfig object.

## Type of change

**Type:** [Update existing documentation /bug/Remove outdated content]

## Related issues/PRs
<!-- 
Link to related issues, feature PRs, or discussions (if applicable)

To automatically close an issue when this PR is merged, use closing
keywords:
- "closes #123" or "fixes #123" or "resolves #123"

For regular references without auto-closing, just use:
- "#123" or "See issue #123"

Examples:
- closes #456 (will auto-close issue #456 when PR is merged)
- See #789 for context (will reference but not auto-close issue #789)
-->
- GitHub issue:
- Feature PR:

<!-- For LangChain employees, if applicable: -->
- Linear issue:
- Slack thread:

## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [x] I have read the [contributing guidelines](README.md)
- [x] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
- [x] I have used **root relative** paths for internal links
- [x] I have updated navigation in `src/docs.json` if needed
- I have gotten approval from the relevant reviewers
- (Internal team members only / optional) I have created a preview
deployment using the [Create Preview Branch
workflow](https://github.com/langchain-ai/docs/actions/workflows/create-preview-branch.yml)

## Additional notes
<!-- Any other information that would be helpful for reviewers -->

---------

Co-authored-by: Lauren Hirata Singh <[email protected]>

Author: mcavdar

src/oss/python/migrate/langchain-v1.mdx

@@ -310,12 +310,16 @@ from langchain.agents.middleware import HumanInTheLoopMiddleware
 agent = create_agent(
     model="claude-sonnet-4-5-20250929",
     tools=[read_email, send_email],
-    middleware=[HumanInTheLoopMiddleware(
-        interrupt_on={
-            "send_email": True,
-            "description": "Please review this email before sending"
-        },
-    )]
+    middleware=[
+        HumanInTheLoopMiddleware(
+            interrupt_on={
+                "send_email": {
+                    "description": "Please review this email before sending",
+                    "allowed_decisions": ["approve", "reject"]
+                }
+            }
+        )
+    ]
 )
 ```