#22157: Add ContextMemory integration guide

Adds documentation for ContextMemory CLI tool for persistent AI coding context memory. npm: https://www.npmjs.com/package/@akashkobal/contextmemory GitHub: https://github.com/AkashKobal/contextmemory <!-- greptile_comment --> <h3>Greptile Summary</h3> Added integration guide for ContextMemory, an optional CLI tool for persisting development context across AI-assisted coding sessions. The documentation follows the existing pattern of standalone integration guides like `brave-search.md`. **Key observations:** - Documentation is clear and well-structured with installation, usage, and MCP integration sections - Tool is properly presented as optional and non-invasive to OpenClaw functionality - Incomplete URLs in the Related Links section need correction - Consider adding `.contextmemory/` to `.gitignore` to prevent accidental commits of local context data <h3>Confidence Score: 4/5</h3> - This PR is safe to merge with minimal risk - it only adds documentation - Documentation-only change with clear presentation of an optional tool. Two minor issues: incomplete URLs in Related Links section and missing `.gitignore` entry recommendation. No code changes, no security concerns, and follows existing documentation patterns. - No files require special attention beyond fixing the incomplete URLs _{Last reviewed commit: f5db45b} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->