docs: add Lians agent memory toolkit

[ebeirne]

Description

Adds a tools integration guide for Lians agent memory, an independently published Apache-2.0 package that provides LangChain tools and LangGraph node factories.

The guide covers:

• zero-setup local SQLite installation
• current recall with superseded facts excluded
• point-in-time recall_at queries
• direct use with create_agent
• checkpoint-aligned recall with the LangGraph node factory

The page follows the current third-party integration policy: implementation remains in the independently maintained lians-sdk package, while this PR adds documentation only.

Package

• PyPI: https://pypi.org/project/lians-sdk/
• Source: https://github.com/Lians-ai/Lians
• License: Apache-2.0

Validation

• followed the current tools integration template and index format
• all examples use the public lians-sdk API
• local examples require no API key or external service
• git diff --check passes
• publication guard confirms no Unicode em dashes in the new guide

[github-actions]

Thanks for opening a docs PR, ebeirne! When it's ready for review, please add the relevant reviewers:

• @mdrxy (Python integrations)

[langchain-oss-automated-triage]

Thanks for contributing a new integration docs page, ebeirne!

We receive a large number of PRs and review them as quickly as we can. Please bear with us as we work through the queue.

If you have already tagged a maintainer on this PR, do not tag them again.

[ebeirne]

Mason Daugherty (@mdrxy) This Python integration documentation is ready for review. All checks are passing. Thank you.