feat: update session manager docs

[JackYPCOnline]

Description

Updates the Session Management documentation page to add full TypeScript SDK coverage alongside the existing Python content.

The TypeScript SDK uses a different, snapshot-based session model compared to Python's message-level persistence. This PR documents that model so TypeScript users have a complete reference.

Key changes:

• Removed the ts_not_supported banner — session management is now supported in the TypeScript SDK
• Added TypeScript tabs throughout: basic usage, FileStorage, S3Storage, storage directory/key structures, and how session management works
• Documented the TypeScript-specific snapshot model: snapshot_latest vs immutable history, saveLatestOn strategy table, snapshotTrigger callback with all SnapshotTriggerParams fields, and loadSnapshotId for restoring from a specific snapshot
• Added a "Custom Storage Backends (TypeScript)" section documenting the SnapshotStorage interface
• Noted TypeScript-specific S3 behavior: bucket must pre-exist, s3Client vs region config options
• Added two TypeScript-specific best practice bullets

Python content is unchanged.

Related Issues

Type of Change

• Content update/revision

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working

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[strands-agent]

Documentation Deployment Complete

Your documentation preview has been successfully deployed!

Preview URL: https://d3ehv1nix5p99z.cloudfront.net/pr-581/

[strands-agent]

Documentation Deployment Complete

Your documentation preview has been successfully deployed!

Preview URL: https://d3ehv1nix5p99z.cloudfront.net/pr-581/

[github-actions]

Issue: Missing space between "systems" and opening parenthesis.

Suggestion: Change to Multi-agent systems (Graph/Swarm)

[github-actions]

Issue: The original Python documentation included a "2. Data Models" subsection that documented the Session, SessionAgent, SessionMessage models and "Multi-Agent State" with links to the API reference. This content appears to have been removed when adding the TypeScript tabs.

Suggestion: Add a second subsection under the Python tab to preserve this documentation. Something like:

    ### 2. Data Models

    Session data is stored using these key data models:

    **Session**

    The [`Session`](../../../api-reference/python/types/session.md#strands.types.session.Session) model is the top-level container...
    
    (rest of the original content)

This is important reference material for Python users understanding the session internals.

[github-actions]

Assessment: Comment

This is excellent documentation work that adds comprehensive TypeScript SDK coverage for session management. The snapshot-based model is well-explained with clear examples for snapshotTrigger, saveLatestOn strategies, and custom storage backends.

Review Summary

• Missing Content: The Python "Data Models" section (documenting Session, SessionAgent, SessionMessage) was removed during the refactoring. This valuable reference material should be preserved in the Python tab.
• Minor: One small formatting issue with a missing space.

The TypeScript-specific additions (snapshot types, persistence triggers table, SnapshotTriggerParams documentation) are thorough and will be very helpful for TypeScript users. Nice work adding the TypeScript-specific best practices at the end!