Add ContextStream to MCP Servers

[escott-]

Summary

Adds ContextStream for the MCP Servers section.

This PR includes .github/CONTEXTSTREAM_LISTING.md with the exact README bullet to add under ### MCP Servers (after AccInt). Happy to move that line into README.md directly in a follow-up commit if preferred.

Suggested README bullet:

- [ContextStream](https://github.com/contextstream/mcp-server) — Durable shared project context and semantic code search for AI coding agents (Cursor, Claude Code, Codex, and more). Hosted MCP + local npx setup. Site: https://contextstream.io · Benchmarks: https://contextstream.io/benchmarks

Links

• GitHub: https://github.com/contextstream/mcp-server
• Website: https://contextstream.io
• Benchmarks: https://contextstream.io/benchmarks
• Hosted MCP: https://mcp.contextstream.io/mcp
• npm: @contextstream/mcp-server

Related: #507

Disclosure: I maintain ContextStream.

[escott-]

Exact README.md edit for maintainers (under ### MCP Servers, after AccInt):

- [ContextStream](https://github.com/contextstream/mcp-server) — Durable shared project context and semantic code search for AI coding agents (Cursor, Claude Code, Codex, and more). Hosted MCP + local npx setup. Site: https://contextstream.io · Benchmarks: https://contextstream.io/benchmarks

I can push that as a direct README commit on this branch if helpful.