Refresh roadmap and maintenance docs

[skippka]

Summary

• add an agent compatibility matrix and link it from the README
• update roadmap status for shipped MCP/cache milestones and add next maintenance items
• expand Secret Guard coverage for GitLab, Stripe, Twilio, and SendGrid-style tokens
• fix package metadata URLs and a Cody preset encoding artifact

GitHub triage

• Open PRs: none
• Reviewed merged PRs: added cody as the coding agent #9, Add MCP wrapper mode #10, Implement provider cache policies #11
• Open issues reviewed: Add optional WASI sandbox runner for high-risk tools #3, Add dashboard screenshot and terminal demo GIF to README #4, Create one-command installer for Windows, macOS, and Linux #5, Add agent compatibility test matrix #6, Expand Secret Guard rule pack #8
• This PR helps with Add agent compatibility test matrix #6 and Expand Secret Guard rule pack #8, and keeps the README roadmap aligned with Add MCP wrapper mode #10/Implement provider cache policies #11

Validation

• python -m unittest discover -s tests using bundled Python: 19 tests passing