docs: add LangChain and LangGraph integration guide

[deepak0x]

Ⅰ. Describe what this PR does

Adds docs/best-practices/use-langchain-langgraph.md, a how-to guide for using OpenKruise Agents' E2B-compatible API from LangChain and LangGraph agents. It mirrors the layout of the existing use-e2b.md and links to the runnable examples/code_interpreter template and the sdk/customized_e2b shim.

The guide covers:

• SDK configuration, including the patch_e2b shim for the private protocol
• A LangChain @tool example that claims a fresh sandbox per call (create_react_agent)
• A LangGraph workflow that keeps a single sandbox alive across tool calls (shared file / variable state)
• Operational notes on pool sizing, the OpenKruise e2b.agents.kruise.io/csi-* metadata keys, and timeout configuration

Ⅱ. Does this pull request fix one issue?

fixes #62

Ⅲ. Describe how to verify it

Render the markdown locally (or via the GitHub PR preview) and confirm:

• All internal links resolve (./use-e2b.md, ../../examples/code_interpreter/sandboxset.yaml, ../../sdk/customized_e2b/README.md).
• Code blocks parse without syntax errors.
• The metadata keys and --e2b-max-timeout flag referenced in the doc match examples/code_interpreter/README.md and cmd/sandbox-manager/main.go:82 respectively.

Ⅳ. Special notes for reviews

Pure docs change — no code touched. The location under docs/best-practices/ follows the existing use-e2b.md precedent and answers the open scoping question @Daiwik-1901 raised in the issue thread.

[kruise-bot]

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[kruise-bot]

Welcome @deepak0x! It looks like this is your first PR to openkruise/agents 🎉

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.69%. Comparing base (edaad73) to head (88f166c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
+ Coverage   74.65%   74.69%   +0.04%     
==========================================
  Files         141      141              
  Lines        9836     9836              
==========================================
+ Hits         7343     7347       +4     
+ Misses       2183     2181       -2     
+ Partials      310      308       -2     

Flag	Coverage Δ
unittests	74.69% <ø> (+0.04%)	⬆️

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